xref: /freebsd/sys/cam/cam_iosched.c (revision 924226fba12cc9a228c73b956e1b7fa24c60b055)
1 /*-
2  * CAM IO Scheduler Interface
3  *
4  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
5  *
6  * Copyright (c) 2015 Netflix, Inc.
7  *
8  * Redistribution and use in source and binary forms, with or without
9  * modification, are permitted provided that the following conditions
10  * are met:
11  * 1. Redistributions of source code must retain the above copyright
12  *    notice, this list of conditions, and the following disclaimer,
13  *    without modification, immediately at the beginning of the file.
14  * 2. The name of the author may not be used to endorse or promote products
15  *    derived from this software without specific prior written permission.
16  *
17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20  * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
21  * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27  * SUCH DAMAGE.
28  *
29  * $FreeBSD$
30  */
31 
32 #include "opt_cam.h"
33 #include "opt_ddb.h"
34 
35 #include <sys/cdefs.h>
36 __FBSDID("$FreeBSD$");
37 
38 #include <sys/param.h>
39 
40 #include <sys/systm.h>
41 #include <sys/kernel.h>
42 #include <sys/bio.h>
43 #include <sys/lock.h>
44 #include <sys/malloc.h>
45 #include <sys/mutex.h>
46 #include <sys/sbuf.h>
47 #include <sys/sysctl.h>
48 
49 #include <cam/cam.h>
50 #include <cam/cam_ccb.h>
51 #include <cam/cam_periph.h>
52 #include <cam/cam_xpt_periph.h>
53 #include <cam/cam_xpt_internal.h>
54 #include <cam/cam_iosched.h>
55 
56 #include <ddb/ddb.h>
57 
58 static MALLOC_DEFINE(M_CAMSCHED, "CAM I/O Scheduler",
59     "CAM I/O Scheduler buffers");
60 
61 static SYSCTL_NODE(_kern_cam, OID_AUTO, iosched, CTLFLAG_RD | CTLFLAG_MPSAFE, 0,
62     "CAM I/O Scheduler parameters");
63 
64 /*
65  * Default I/O scheduler for FreeBSD. This implementation is just a thin-vineer
66  * over the bioq_* interface, with notions of separate calls for normal I/O and
67  * for trims.
68  *
69  * When CAM_IOSCHED_DYNAMIC is defined, the scheduler is enhanced to dynamically
70  * steer the rate of one type of traffic to help other types of traffic (eg
71  * limit writes when read latency deteriorates on SSDs).
72  */
73 
74 #ifdef CAM_IOSCHED_DYNAMIC
75 
76 static bool do_dynamic_iosched = true;
77 SYSCTL_BOOL(_kern_cam_iosched, OID_AUTO, dynamic, CTLFLAG_RD | CTLFLAG_TUN,
78     &do_dynamic_iosched, 1,
79     "Enable Dynamic I/O scheduler optimizations.");
80 
81 /*
82  * For an EMA, with an alpha of alpha, we know
83  * 	alpha = 2 / (N + 1)
84  * or
85  * 	N = 1 + (2 / alpha)
86  * where N is the number of samples that 86% of the current
87  * EMA is derived from.
88  *
89  * So we invent[*] alpha_bits:
90  *	alpha_bits = -log_2(alpha)
91  *	alpha = 2^-alpha_bits
92  * So
93  *	N = 1 + 2^(alpha_bits + 1)
94  *
95  * The default 9 gives a 1025 lookback for 86% of the data.
96  * For a brief intro: https://en.wikipedia.org/wiki/Moving_average
97  *
98  * [*] Steal from the load average code and many other places.
99  * Note: See computation of EMA and EMVAR for acceptable ranges of alpha.
100  */
101 static int alpha_bits = 9;
102 SYSCTL_INT(_kern_cam_iosched, OID_AUTO, alpha_bits, CTLFLAG_RW | CTLFLAG_TUN,
103     &alpha_bits, 1,
104     "Bits in EMA's alpha.");
105 
106 /*
107  * Different parameters for the buckets of latency we keep track of. These are all
108  * published read-only since at present they are compile time constants.
109  *
110  * Bucket base is the upper bounds of the first latency bucket. It's currently 20us.
111  * With 20 buckets (see below), that leads to a geometric progression with a max size
112  * of 5.2s which is safeily larger than 1s to help diagnose extreme outliers better.
113  */
114 #ifndef BUCKET_BASE
115 #define BUCKET_BASE ((SBT_1S / 50000) + 1)	/* 20us */
116 #endif
117 static sbintime_t bucket_base = BUCKET_BASE;
118 SYSCTL_SBINTIME_USEC(_kern_cam_iosched, OID_AUTO, bucket_base_us, CTLFLAG_RD,
119     &bucket_base,
120     "Size of the smallest latency bucket");
121 
122 /*
123  * Bucket ratio is the geometric progression for the bucket. For a bucket b_n
124  * the size of bucket b_n+1 is b_n * bucket_ratio / 100.
125  */
126 static int bucket_ratio = 200;	/* Rather hard coded at the moment */
127 SYSCTL_INT(_kern_cam_iosched, OID_AUTO, bucket_ratio, CTLFLAG_RD,
128     &bucket_ratio, 200,
129     "Latency Bucket Ratio for geometric progression.");
130 
131 /*
132  * Number of total buckets. Starting at BUCKET_BASE, each one is a power of 2.
133  */
134 #ifndef LAT_BUCKETS
135 #define LAT_BUCKETS 20	/* < 20us < 40us ... < 2^(n-1)*20us >= 2^(n-1)*20us */
136 #endif
137 static int lat_buckets = LAT_BUCKETS;
138 SYSCTL_INT(_kern_cam_iosched, OID_AUTO, buckets, CTLFLAG_RD,
139     &lat_buckets, LAT_BUCKETS,
140     "Total number of latency buckets published");
141 
142 /*
143  * Read bias: how many reads do we favor before scheduling a write
144  * when we have a choice.
145  */
146 static int default_read_bias = 0;
147 SYSCTL_INT(_kern_cam_iosched, OID_AUTO, read_bias, CTLFLAG_RWTUN,
148     &default_read_bias, 0,
149     "Default read bias for new devices.");
150 
151 struct iop_stats;
152 struct cam_iosched_softc;
153 
154 int iosched_debug = 0;
155 
156 typedef enum {
157 	none = 0,				/* No limits */
158 	queue_depth,			/* Limit how many ops we queue to SIM */
159 	iops,				/* Limit # of IOPS to the drive */
160 	bandwidth,			/* Limit bandwidth to the drive */
161 	limiter_max
162 } io_limiter;
163 
164 static const char *cam_iosched_limiter_names[] =
165     { "none", "queue_depth", "iops", "bandwidth" };
166 
167 /*
168  * Called to initialize the bits of the iop_stats structure relevant to the
169  * limiter. Called just after the limiter is set.
170  */
171 typedef int l_init_t(struct iop_stats *);
172 
173 /*
174  * Called every tick.
175  */
176 typedef int l_tick_t(struct iop_stats *);
177 
178 /*
179  * Called to see if the limiter thinks this IOP can be allowed to
180  * proceed. If so, the limiter assumes that the IOP proceeded
181  * and makes any accounting of it that's needed.
182  */
183 typedef int l_iop_t(struct iop_stats *, struct bio *);
184 
185 /*
186  * Called when an I/O completes so the limiter can update its
187  * accounting. Pending I/Os may complete in any order (even when
188  * sent to the hardware at the same time), so the limiter may not
189  * make any assumptions other than this I/O has completed. If it
190  * returns 1, then xpt_schedule() needs to be called again.
191  */
192 typedef int l_iodone_t(struct iop_stats *, struct bio *);
193 
194 static l_iop_t cam_iosched_qd_iop;
195 static l_iop_t cam_iosched_qd_caniop;
196 static l_iodone_t cam_iosched_qd_iodone;
197 
198 static l_init_t cam_iosched_iops_init;
199 static l_tick_t cam_iosched_iops_tick;
200 static l_iop_t cam_iosched_iops_caniop;
201 static l_iop_t cam_iosched_iops_iop;
202 
203 static l_init_t cam_iosched_bw_init;
204 static l_tick_t cam_iosched_bw_tick;
205 static l_iop_t cam_iosched_bw_caniop;
206 static l_iop_t cam_iosched_bw_iop;
207 
208 struct limswitch {
209 	l_init_t	*l_init;
210 	l_tick_t	*l_tick;
211 	l_iop_t		*l_iop;
212 	l_iop_t		*l_caniop;
213 	l_iodone_t	*l_iodone;
214 } limsw[] =
215 {
216 	{	/* none */
217 		.l_init = NULL,
218 		.l_tick = NULL,
219 		.l_iop = NULL,
220 		.l_iodone= NULL,
221 	},
222 	{	/* queue_depth */
223 		.l_init = NULL,
224 		.l_tick = NULL,
225 		.l_caniop = cam_iosched_qd_caniop,
226 		.l_iop = cam_iosched_qd_iop,
227 		.l_iodone= cam_iosched_qd_iodone,
228 	},
229 	{	/* iops */
230 		.l_init = cam_iosched_iops_init,
231 		.l_tick = cam_iosched_iops_tick,
232 		.l_caniop = cam_iosched_iops_caniop,
233 		.l_iop = cam_iosched_iops_iop,
234 		.l_iodone= NULL,
235 	},
236 	{	/* bandwidth */
237 		.l_init = cam_iosched_bw_init,
238 		.l_tick = cam_iosched_bw_tick,
239 		.l_caniop = cam_iosched_bw_caniop,
240 		.l_iop = cam_iosched_bw_iop,
241 		.l_iodone= NULL,
242 	},
243 };
244 
245 struct iop_stats {
246 	/*
247 	 * sysctl state for this subnode.
248 	 */
249 	struct sysctl_ctx_list	sysctl_ctx;
250 	struct sysctl_oid	*sysctl_tree;
251 
252 	/*
253 	 * Information about the current rate limiters, if any
254 	 */
255 	io_limiter	limiter;	/* How are I/Os being limited */
256 	int		min;		/* Low range of limit */
257 	int		max;		/* High range of limit */
258 	int		current;	/* Current rate limiter */
259 	int		l_value1;	/* per-limiter scratch value 1. */
260 	int		l_value2;	/* per-limiter scratch value 2. */
261 
262 	/*
263 	 * Debug information about counts of I/Os that have gone through the
264 	 * scheduler.
265 	 */
266 	int		pending;	/* I/Os pending in the hardware */
267 	int		queued;		/* number currently in the queue */
268 	int		total;		/* Total for all time -- wraps */
269 	int		in;		/* number queued all time -- wraps */
270 	int		out;		/* number completed all time -- wraps */
271 	int		errs;		/* Number of I/Os completed with error --  wraps */
272 
273 	/*
274 	 * Statistics on different bits of the process.
275 	 */
276 		/* Exp Moving Average, see alpha_bits for more details */
277 	sbintime_t      ema;
278 	sbintime_t      emvar;
279 	sbintime_t      sd;		/* Last computed sd */
280 
281 	uint32_t	state_flags;
282 #define IOP_RATE_LIMITED		1u
283 
284 	uint64_t	latencies[LAT_BUCKETS];
285 
286 	struct cam_iosched_softc *softc;
287 };
288 
289 typedef enum {
290 	set_max = 0,			/* current = max */
291 	read_latency,			/* Steer read latency by throttling writes */
292 	cl_max				/* Keep last */
293 } control_type;
294 
295 static const char *cam_iosched_control_type_names[] =
296     { "set_max", "read_latency" };
297 
298 struct control_loop {
299 	/*
300 	 * sysctl state for this subnode.
301 	 */
302 	struct sysctl_ctx_list	sysctl_ctx;
303 	struct sysctl_oid	*sysctl_tree;
304 
305 	sbintime_t	next_steer;		/* Time of next steer */
306 	sbintime_t	steer_interval;		/* How often do we steer? */
307 	sbintime_t	lolat;
308 	sbintime_t	hilat;
309 	int		alpha;
310 	control_type	type;			/* What type of control? */
311 	int		last_count;		/* Last I/O count */
312 
313 	struct cam_iosched_softc *softc;
314 };
315 
316 #endif
317 
318 struct cam_iosched_softc {
319 	struct bio_queue_head bio_queue;
320 	struct bio_queue_head trim_queue;
321 				/* scheduler flags < 16, user flags >= 16 */
322 	uint32_t	flags;
323 	int		sort_io_queue;
324 	int		trim_goal;		/* # of trims to queue before sending */
325 	int		trim_ticks;		/* Max ticks to hold trims */
326 	int		last_trim_tick;		/* Last 'tick' time ld a trim */
327 	int		queued_trims;		/* Number of trims in the queue */
328 #ifdef CAM_IOSCHED_DYNAMIC
329 	int		read_bias;		/* Read bias setting */
330 	int		current_read_bias;	/* Current read bias state */
331 	int		total_ticks;
332 	int		load;			/* EMA of 'load average' of disk / 2^16 */
333 
334 	struct bio_queue_head write_queue;
335 	struct iop_stats read_stats, write_stats, trim_stats;
336 	struct sysctl_ctx_list	sysctl_ctx;
337 	struct sysctl_oid	*sysctl_tree;
338 
339 	int		quanta;			/* Number of quanta per second */
340 	struct callout	ticker;			/* Callout for our quota system */
341 	struct cam_periph *periph;		/* cam periph associated with this device */
342 	uint32_t	this_frac;		/* Fraction of a second (1024ths) for this tick */
343 	sbintime_t	last_time;		/* Last time we ticked */
344 	struct control_loop cl;
345 	sbintime_t	max_lat;		/* when != 0, if iop latency > max_lat, call max_lat_fcn */
346 	cam_iosched_latfcn_t	latfcn;
347 	void		*latarg;
348 #endif
349 };
350 
351 #ifdef CAM_IOSCHED_DYNAMIC
352 /*
353  * helper functions to call the limsw functions.
354  */
355 static int
356 cam_iosched_limiter_init(struct iop_stats *ios)
357 {
358 	int lim = ios->limiter;
359 
360 	/* maybe this should be a kassert */
361 	if (lim < none || lim >= limiter_max)
362 		return EINVAL;
363 
364 	if (limsw[lim].l_init)
365 		return limsw[lim].l_init(ios);
366 
367 	return 0;
368 }
369 
370 static int
371 cam_iosched_limiter_tick(struct iop_stats *ios)
372 {
373 	int lim = ios->limiter;
374 
375 	/* maybe this should be a kassert */
376 	if (lim < none || lim >= limiter_max)
377 		return EINVAL;
378 
379 	if (limsw[lim].l_tick)
380 		return limsw[lim].l_tick(ios);
381 
382 	return 0;
383 }
384 
385 static int
386 cam_iosched_limiter_iop(struct iop_stats *ios, struct bio *bp)
387 {
388 	int lim = ios->limiter;
389 
390 	/* maybe this should be a kassert */
391 	if (lim < none || lim >= limiter_max)
392 		return EINVAL;
393 
394 	if (limsw[lim].l_iop)
395 		return limsw[lim].l_iop(ios, bp);
396 
397 	return 0;
398 }
399 
400 static int
401 cam_iosched_limiter_caniop(struct iop_stats *ios, struct bio *bp)
402 {
403 	int lim = ios->limiter;
404 
405 	/* maybe this should be a kassert */
406 	if (lim < none || lim >= limiter_max)
407 		return EINVAL;
408 
409 	if (limsw[lim].l_caniop)
410 		return limsw[lim].l_caniop(ios, bp);
411 
412 	return 0;
413 }
414 
415 static int
416 cam_iosched_limiter_iodone(struct iop_stats *ios, struct bio *bp)
417 {
418 	int lim = ios->limiter;
419 
420 	/* maybe this should be a kassert */
421 	if (lim < none || lim >= limiter_max)
422 		return 0;
423 
424 	if (limsw[lim].l_iodone)
425 		return limsw[lim].l_iodone(ios, bp);
426 
427 	return 0;
428 }
429 
430 /*
431  * Functions to implement the different kinds of limiters
432  */
433 
434 static int
435 cam_iosched_qd_iop(struct iop_stats *ios, struct bio *bp)
436 {
437 
438 	if (ios->current <= 0 || ios->pending < ios->current)
439 		return 0;
440 
441 	return EAGAIN;
442 }
443 
444 static int
445 cam_iosched_qd_caniop(struct iop_stats *ios, struct bio *bp)
446 {
447 
448 	if (ios->current <= 0 || ios->pending < ios->current)
449 		return 0;
450 
451 	return EAGAIN;
452 }
453 
454 static int
455 cam_iosched_qd_iodone(struct iop_stats *ios, struct bio *bp)
456 {
457 
458 	if (ios->current <= 0 || ios->pending != ios->current)
459 		return 0;
460 
461 	return 1;
462 }
463 
464 static int
465 cam_iosched_iops_init(struct iop_stats *ios)
466 {
467 
468 	ios->l_value1 = ios->current / ios->softc->quanta;
469 	if (ios->l_value1 <= 0)
470 		ios->l_value1 = 1;
471 	ios->l_value2 = 0;
472 
473 	return 0;
474 }
475 
476 static int
477 cam_iosched_iops_tick(struct iop_stats *ios)
478 {
479 	int new_ios;
480 
481 	/*
482 	 * Allow at least one IO per tick until all
483 	 * the IOs for this interval have been spent.
484 	 */
485 	new_ios = (int)((ios->current * (uint64_t)ios->softc->this_frac) >> 16);
486 	if (new_ios < 1 && ios->l_value2 < ios->current) {
487 		new_ios = 1;
488 		ios->l_value2++;
489 	}
490 
491 	/*
492 	 * If this a new accounting interval, discard any "unspent" ios
493 	 * granted in the previous interval.  Otherwise add the new ios to
494 	 * the previously granted ones that haven't been spent yet.
495 	 */
496 	if ((ios->softc->total_ticks % ios->softc->quanta) == 0) {
497 		ios->l_value1 = new_ios;
498 		ios->l_value2 = 1;
499 	} else {
500 		ios->l_value1 += new_ios;
501 	}
502 
503 	return 0;
504 }
505 
506 static int
507 cam_iosched_iops_caniop(struct iop_stats *ios, struct bio *bp)
508 {
509 
510 	/*
511 	 * So if we have any more IOPs left, allow it,
512 	 * otherwise wait. If current iops is 0, treat that
513 	 * as unlimited as a failsafe.
514 	 */
515 	if (ios->current > 0 && ios->l_value1 <= 0)
516 		return EAGAIN;
517 	return 0;
518 }
519 
520 static int
521 cam_iosched_iops_iop(struct iop_stats *ios, struct bio *bp)
522 {
523 	int rv;
524 
525 	rv = cam_iosched_limiter_caniop(ios, bp);
526 	if (rv == 0)
527 		ios->l_value1--;
528 
529 	return rv;
530 }
531 
532 static int
533 cam_iosched_bw_init(struct iop_stats *ios)
534 {
535 
536 	/* ios->current is in kB/s, so scale to bytes */
537 	ios->l_value1 = ios->current * 1000 / ios->softc->quanta;
538 
539 	return 0;
540 }
541 
542 static int
543 cam_iosched_bw_tick(struct iop_stats *ios)
544 {
545 	int bw;
546 
547 	/*
548 	 * If we're in the hole for available quota from
549 	 * the last time, then add the quantum for this.
550 	 * If we have any left over from last quantum,
551 	 * then too bad, that's lost. Also, ios->current
552 	 * is in kB/s, so scale.
553 	 *
554 	 * We also allow up to 4 quanta of credits to
555 	 * accumulate to deal with burstiness. 4 is extremely
556 	 * arbitrary.
557 	 */
558 	bw = (int)((ios->current * 1000ull * (uint64_t)ios->softc->this_frac) >> 16);
559 	if (ios->l_value1 < bw * 4)
560 		ios->l_value1 += bw;
561 
562 	return 0;
563 }
564 
565 static int
566 cam_iosched_bw_caniop(struct iop_stats *ios, struct bio *bp)
567 {
568 	/*
569 	 * So if we have any more bw quota left, allow it,
570 	 * otherwise wait. Note, we'll go negative and that's
571 	 * OK. We'll just get a little less next quota.
572 	 *
573 	 * Note on going negative: that allows us to process
574 	 * requests in order better, since we won't allow
575 	 * shorter reads to get around the long one that we
576 	 * don't have the quota to do just yet. It also prevents
577 	 * starvation by being a little more permissive about
578 	 * what we let through this quantum (to prevent the
579 	 * starvation), at the cost of getting a little less
580 	 * next quantum.
581 	 *
582 	 * Also note that if the current limit is <= 0,
583 	 * we treat it as unlimited as a failsafe.
584 	 */
585 	if (ios->current > 0 && ios->l_value1 <= 0)
586 		return EAGAIN;
587 
588 	return 0;
589 }
590 
591 static int
592 cam_iosched_bw_iop(struct iop_stats *ios, struct bio *bp)
593 {
594 	int rv;
595 
596 	rv = cam_iosched_limiter_caniop(ios, bp);
597 	if (rv == 0)
598 		ios->l_value1 -= bp->bio_length;
599 
600 	return rv;
601 }
602 
603 static void cam_iosched_cl_maybe_steer(struct control_loop *clp);
604 
605 static void
606 cam_iosched_ticker(void *arg)
607 {
608 	struct cam_iosched_softc *isc = arg;
609 	sbintime_t now, delta;
610 	int pending;
611 
612 	callout_reset(&isc->ticker, hz / isc->quanta, cam_iosched_ticker, isc);
613 
614 	now = sbinuptime();
615 	delta = now - isc->last_time;
616 	isc->this_frac = (uint32_t)delta >> 16;		/* Note: discards seconds -- should be 0 harmless if not */
617 	isc->last_time = now;
618 
619 	cam_iosched_cl_maybe_steer(&isc->cl);
620 
621 	cam_iosched_limiter_tick(&isc->read_stats);
622 	cam_iosched_limiter_tick(&isc->write_stats);
623 	cam_iosched_limiter_tick(&isc->trim_stats);
624 
625 	cam_iosched_schedule(isc, isc->periph);
626 
627 	/*
628 	 * isc->load is an EMA of the pending I/Os at each tick. The number of
629 	 * pending I/Os is the sum of the I/Os queued to the hardware, and those
630 	 * in the software queue that could be queued to the hardware if there
631 	 * were slots.
632 	 *
633 	 * ios_stats.pending is a count of requests in the SIM right now for
634 	 * each of these types of I/O. So the total pending count is the sum of
635 	 * these I/Os and the sum of the queued I/Os still in the software queue
636 	 * for those operations that aren't being rate limited at the moment.
637 	 *
638 	 * The reason for the rate limiting bit is because those I/Os
639 	 * aren't part of the software queued load (since we could
640 	 * give them to hardware, but choose not to).
641 	 *
642 	 * Note: due to a bug in counting pending TRIM in the device, we
643 	 * don't include them in this count. We count each BIO_DELETE in
644 	 * the pending count, but the periph drivers collapse them down
645 	 * into one TRIM command. That one trim command gets the completion
646 	 * so the counts get off.
647 	 */
648 	pending = isc->read_stats.pending + isc->write_stats.pending /* + isc->trim_stats.pending */;
649 	pending += !!(isc->read_stats.state_flags & IOP_RATE_LIMITED) * isc->read_stats.queued +
650 	    !!(isc->write_stats.state_flags & IOP_RATE_LIMITED) * isc->write_stats.queued /* +
651 	    !!(isc->trim_stats.state_flags & IOP_RATE_LIMITED) * isc->trim_stats.queued */ ;
652 	pending <<= 16;
653 	pending /= isc->periph->path->device->ccbq.total_openings;
654 
655 	isc->load = (pending + (isc->load << 13) - isc->load) >> 13; /* see above: 13 -> 16139 / 200/s = ~81s ~1 minute */
656 
657 	isc->total_ticks++;
658 }
659 
660 static void
661 cam_iosched_cl_init(struct control_loop *clp, struct cam_iosched_softc *isc)
662 {
663 
664 	clp->next_steer = sbinuptime();
665 	clp->softc = isc;
666 	clp->steer_interval = SBT_1S * 5;	/* Let's start out steering every 5s */
667 	clp->lolat = 5 * SBT_1MS;
668 	clp->hilat = 15 * SBT_1MS;
669 	clp->alpha = 20;			/* Alpha == gain. 20 = .2 */
670 	clp->type = set_max;
671 }
672 
673 static void
674 cam_iosched_cl_maybe_steer(struct control_loop *clp)
675 {
676 	struct cam_iosched_softc *isc;
677 	sbintime_t now, lat;
678 	int old;
679 
680 	isc = clp->softc;
681 	now = isc->last_time;
682 	if (now < clp->next_steer)
683 		return;
684 
685 	clp->next_steer = now + clp->steer_interval;
686 	switch (clp->type) {
687 	case set_max:
688 		if (isc->write_stats.current != isc->write_stats.max)
689 			printf("Steering write from %d kBps to %d kBps\n",
690 			    isc->write_stats.current, isc->write_stats.max);
691 		isc->read_stats.current = isc->read_stats.max;
692 		isc->write_stats.current = isc->write_stats.max;
693 		isc->trim_stats.current = isc->trim_stats.max;
694 		break;
695 	case read_latency:
696 		old = isc->write_stats.current;
697 		lat = isc->read_stats.ema;
698 		/*
699 		 * Simple PLL-like engine. Since we're steering to a range for
700 		 * the SP (set point) that makes things a little more
701 		 * complicated. In addition, we're not directly controlling our
702 		 * PV (process variable), the read latency, but instead are
703 		 * manipulating the write bandwidth limit for our MV
704 		 * (manipulation variable), analysis of this code gets a bit
705 		 * messy. Also, the MV is a very noisy control surface for read
706 		 * latency since it is affected by many hidden processes inside
707 		 * the device which change how responsive read latency will be
708 		 * in reaction to changes in write bandwidth. Unlike the classic
709 		 * boiler control PLL. this may result in over-steering while
710 		 * the SSD takes its time to react to the new, lower load. This
711 		 * is why we use a relatively low alpha of between .1 and .25 to
712 		 * compensate for this effect. At .1, it takes ~22 steering
713 		 * intervals to back off by a factor of 10. At .2 it only takes
714 		 * ~10. At .25 it only takes ~8. However some preliminary data
715 		 * from the SSD drives suggests a reasponse time in 10's of
716 		 * seconds before latency drops regardless of the new write
717 		 * rate. Careful observation will be required to tune this
718 		 * effectively.
719 		 *
720 		 * Also, when there's no read traffic, we jack up the write
721 		 * limit too regardless of the last read latency.  10 is
722 		 * somewhat arbitrary.
723 		 */
724 		if (lat < clp->lolat || isc->read_stats.total - clp->last_count < 10)
725 			isc->write_stats.current = isc->write_stats.current *
726 			    (100 + clp->alpha) / 100;	/* Scale up */
727 		else if (lat > clp->hilat)
728 			isc->write_stats.current = isc->write_stats.current *
729 			    (100 - clp->alpha) / 100;	/* Scale down */
730 		clp->last_count = isc->read_stats.total;
731 
732 		/*
733 		 * Even if we don't steer, per se, enforce the min/max limits as
734 		 * those may have changed.
735 		 */
736 		if (isc->write_stats.current < isc->write_stats.min)
737 			isc->write_stats.current = isc->write_stats.min;
738 		if (isc->write_stats.current > isc->write_stats.max)
739 			isc->write_stats.current = isc->write_stats.max;
740 		if (old != isc->write_stats.current && 	iosched_debug)
741 			printf("Steering write from %d kBps to %d kBps due to latency of %jdus\n",
742 			    old, isc->write_stats.current,
743 			    (uintmax_t)((uint64_t)1000000 * (uint32_t)lat) >> 32);
744 		break;
745 	case cl_max:
746 		break;
747 	}
748 }
749 #endif
750 
751 /*
752  * Trim or similar currently pending completion. Should only be set for
753  * those drivers wishing only one Trim active at a time.
754  */
755 #define CAM_IOSCHED_FLAG_TRIM_ACTIVE	(1ul << 0)
756 			/* Callout active, and needs to be torn down */
757 #define CAM_IOSCHED_FLAG_CALLOUT_ACTIVE (1ul << 1)
758 
759 			/* Periph drivers set these flags to indicate work */
760 #define CAM_IOSCHED_FLAG_WORK_FLAGS	((0xffffu) << 16)
761 
762 #ifdef CAM_IOSCHED_DYNAMIC
763 static void
764 cam_iosched_io_metric_update(struct cam_iosched_softc *isc,
765     sbintime_t sim_latency, int cmd, size_t size);
766 #endif
767 
768 static inline bool
769 cam_iosched_has_flagged_work(struct cam_iosched_softc *isc)
770 {
771 	return !!(isc->flags & CAM_IOSCHED_FLAG_WORK_FLAGS);
772 }
773 
774 static inline bool
775 cam_iosched_has_io(struct cam_iosched_softc *isc)
776 {
777 #ifdef CAM_IOSCHED_DYNAMIC
778 	if (do_dynamic_iosched) {
779 		struct bio *rbp = bioq_first(&isc->bio_queue);
780 		struct bio *wbp = bioq_first(&isc->write_queue);
781 		bool can_write = wbp != NULL &&
782 		    cam_iosched_limiter_caniop(&isc->write_stats, wbp) == 0;
783 		bool can_read = rbp != NULL &&
784 		    cam_iosched_limiter_caniop(&isc->read_stats, rbp) == 0;
785 		if (iosched_debug > 2) {
786 			printf("can write %d: pending_writes %d max_writes %d\n", can_write, isc->write_stats.pending, isc->write_stats.max);
787 			printf("can read %d: read_stats.pending %d max_reads %d\n", can_read, isc->read_stats.pending, isc->read_stats.max);
788 			printf("Queued reads %d writes %d\n", isc->read_stats.queued, isc->write_stats.queued);
789 		}
790 		return can_read || can_write;
791 	}
792 #endif
793 	return bioq_first(&isc->bio_queue) != NULL;
794 }
795 
796 static inline bool
797 cam_iosched_has_more_trim(struct cam_iosched_softc *isc)
798 {
799 	struct bio *bp;
800 
801 	bp = bioq_first(&isc->trim_queue);
802 #ifdef CAM_IOSCHED_DYNAMIC
803 	if (do_dynamic_iosched) {
804 		/*
805 		 * If we're limiting trims, then defer action on trims
806 		 * for a bit.
807 		 */
808 		if (bp == NULL || cam_iosched_limiter_caniop(&isc->trim_stats, bp) != 0)
809 			return false;
810 	}
811 #endif
812 
813 	/*
814 	 * If we've set a trim_goal, then if we exceed that allow trims
815 	 * to be passed back to the driver. If we've also set a tick timeout
816 	 * allow trims back to the driver. Otherwise, don't allow trims yet.
817 	 */
818 	if (isc->trim_goal > 0) {
819 		if (isc->queued_trims >= isc->trim_goal)
820 			return true;
821 		if (isc->queued_trims > 0 &&
822 		    isc->trim_ticks > 0 &&
823 		    ticks - isc->last_trim_tick > isc->trim_ticks)
824 			return true;
825 		return false;
826 	}
827 
828 	/* NB: Should perhaps have a max trim active independent of I/O limiters */
829 	return !(isc->flags & CAM_IOSCHED_FLAG_TRIM_ACTIVE) && bp != NULL;
830 }
831 
832 #define cam_iosched_sort_queue(isc)	((isc)->sort_io_queue >= 0 ?	\
833     (isc)->sort_io_queue : cam_sort_io_queues)
834 
835 static inline bool
836 cam_iosched_has_work(struct cam_iosched_softc *isc)
837 {
838 #ifdef CAM_IOSCHED_DYNAMIC
839 	if (iosched_debug > 2)
840 		printf("has work: %d %d %d\n", cam_iosched_has_io(isc),
841 		    cam_iosched_has_more_trim(isc),
842 		    cam_iosched_has_flagged_work(isc));
843 #endif
844 
845 	return cam_iosched_has_io(isc) ||
846 		cam_iosched_has_more_trim(isc) ||
847 		cam_iosched_has_flagged_work(isc);
848 }
849 
850 #ifdef CAM_IOSCHED_DYNAMIC
851 static void
852 cam_iosched_iop_stats_init(struct cam_iosched_softc *isc, struct iop_stats *ios)
853 {
854 
855 	ios->limiter = none;
856 	ios->in = 0;
857 	ios->max = ios->current = 300000;
858 	ios->min = 1;
859 	ios->out = 0;
860 	ios->errs = 0;
861 	ios->pending = 0;
862 	ios->queued = 0;
863 	ios->total = 0;
864 	ios->ema = 0;
865 	ios->emvar = 0;
866 	ios->softc = isc;
867 	cam_iosched_limiter_init(ios);
868 }
869 
870 static int
871 cam_iosched_limiter_sysctl(SYSCTL_HANDLER_ARGS)
872 {
873 	char buf[16];
874 	struct iop_stats *ios;
875 	struct cam_iosched_softc *isc;
876 	int value, i, error;
877 	const char *p;
878 
879 	ios = arg1;
880 	isc = ios->softc;
881 	value = ios->limiter;
882 	if (value < none || value >= limiter_max)
883 		p = "UNKNOWN";
884 	else
885 		p = cam_iosched_limiter_names[value];
886 
887 	strlcpy(buf, p, sizeof(buf));
888 	error = sysctl_handle_string(oidp, buf, sizeof(buf), req);
889 	if (error != 0 || req->newptr == NULL)
890 		return error;
891 
892 	cam_periph_lock(isc->periph);
893 
894 	for (i = none; i < limiter_max; i++) {
895 		if (strcmp(buf, cam_iosched_limiter_names[i]) != 0)
896 			continue;
897 		ios->limiter = i;
898 		error = cam_iosched_limiter_init(ios);
899 		if (error != 0) {
900 			ios->limiter = value;
901 			cam_periph_unlock(isc->periph);
902 			return error;
903 		}
904 		/* Note: disk load averate requires ticker to be always running */
905 		callout_reset(&isc->ticker, hz / isc->quanta, cam_iosched_ticker, isc);
906 		isc->flags |= CAM_IOSCHED_FLAG_CALLOUT_ACTIVE;
907 
908 		cam_periph_unlock(isc->periph);
909 		return 0;
910 	}
911 
912 	cam_periph_unlock(isc->periph);
913 	return EINVAL;
914 }
915 
916 static int
917 cam_iosched_control_type_sysctl(SYSCTL_HANDLER_ARGS)
918 {
919 	char buf[16];
920 	struct control_loop *clp;
921 	struct cam_iosched_softc *isc;
922 	int value, i, error;
923 	const char *p;
924 
925 	clp = arg1;
926 	isc = clp->softc;
927 	value = clp->type;
928 	if (value < none || value >= cl_max)
929 		p = "UNKNOWN";
930 	else
931 		p = cam_iosched_control_type_names[value];
932 
933 	strlcpy(buf, p, sizeof(buf));
934 	error = sysctl_handle_string(oidp, buf, sizeof(buf), req);
935 	if (error != 0 || req->newptr == NULL)
936 		return error;
937 
938 	for (i = set_max; i < cl_max; i++) {
939 		if (strcmp(buf, cam_iosched_control_type_names[i]) != 0)
940 			continue;
941 		cam_periph_lock(isc->periph);
942 		clp->type = i;
943 		cam_periph_unlock(isc->periph);
944 		return 0;
945 	}
946 
947 	return EINVAL;
948 }
949 
950 static int
951 cam_iosched_sbintime_sysctl(SYSCTL_HANDLER_ARGS)
952 {
953 	char buf[16];
954 	sbintime_t value;
955 	int error;
956 	uint64_t us;
957 
958 	value = *(sbintime_t *)arg1;
959 	us = (uint64_t)value / SBT_1US;
960 	snprintf(buf, sizeof(buf), "%ju", (intmax_t)us);
961 	error = sysctl_handle_string(oidp, buf, sizeof(buf), req);
962 	if (error != 0 || req->newptr == NULL)
963 		return error;
964 	us = strtoul(buf, NULL, 10);
965 	if (us == 0)
966 		return EINVAL;
967 	*(sbintime_t *)arg1 = us * SBT_1US;
968 	return 0;
969 }
970 
971 static int
972 cam_iosched_sysctl_latencies(SYSCTL_HANDLER_ARGS)
973 {
974 	int i, error;
975 	struct sbuf sb;
976 	uint64_t *latencies;
977 
978 	latencies = arg1;
979 	sbuf_new_for_sysctl(&sb, NULL, LAT_BUCKETS * 16, req);
980 
981 	for (i = 0; i < LAT_BUCKETS - 1; i++)
982 		sbuf_printf(&sb, "%jd,", (intmax_t)latencies[i]);
983 	sbuf_printf(&sb, "%jd", (intmax_t)latencies[LAT_BUCKETS - 1]);
984 	error = sbuf_finish(&sb);
985 	sbuf_delete(&sb);
986 
987 	return (error);
988 }
989 
990 static int
991 cam_iosched_quanta_sysctl(SYSCTL_HANDLER_ARGS)
992 {
993 	int *quanta;
994 	int error, value;
995 
996 	quanta = (unsigned *)arg1;
997 	value = *quanta;
998 
999 	error = sysctl_handle_int(oidp, (int *)&value, 0, req);
1000 	if ((error != 0) || (req->newptr == NULL))
1001 		return (error);
1002 
1003 	if (value < 1 || value > hz)
1004 		return (EINVAL);
1005 
1006 	*quanta = value;
1007 
1008 	return (0);
1009 }
1010 
1011 static void
1012 cam_iosched_iop_stats_sysctl_init(struct cam_iosched_softc *isc, struct iop_stats *ios, char *name)
1013 {
1014 	struct sysctl_oid_list *n;
1015 	struct sysctl_ctx_list *ctx;
1016 
1017 	ios->sysctl_tree = SYSCTL_ADD_NODE(&isc->sysctl_ctx,
1018 	    SYSCTL_CHILDREN(isc->sysctl_tree), OID_AUTO, name,
1019 	    CTLFLAG_RD | CTLFLAG_MPSAFE, 0, name);
1020 	n = SYSCTL_CHILDREN(ios->sysctl_tree);
1021 	ctx = &ios->sysctl_ctx;
1022 
1023 	SYSCTL_ADD_UQUAD(ctx, n,
1024 	    OID_AUTO, "ema", CTLFLAG_RD,
1025 	    &ios->ema,
1026 	    "Fast Exponentially Weighted Moving Average");
1027 	SYSCTL_ADD_UQUAD(ctx, n,
1028 	    OID_AUTO, "emvar", CTLFLAG_RD,
1029 	    &ios->emvar,
1030 	    "Fast Exponentially Weighted Moving Variance");
1031 
1032 	SYSCTL_ADD_INT(ctx, n,
1033 	    OID_AUTO, "pending", CTLFLAG_RD,
1034 	    &ios->pending, 0,
1035 	    "Instantaneous # of pending transactions");
1036 	SYSCTL_ADD_INT(ctx, n,
1037 	    OID_AUTO, "count", CTLFLAG_RD,
1038 	    &ios->total, 0,
1039 	    "# of transactions submitted to hardware");
1040 	SYSCTL_ADD_INT(ctx, n,
1041 	    OID_AUTO, "queued", CTLFLAG_RD,
1042 	    &ios->queued, 0,
1043 	    "# of transactions in the queue");
1044 	SYSCTL_ADD_INT(ctx, n,
1045 	    OID_AUTO, "in", CTLFLAG_RD,
1046 	    &ios->in, 0,
1047 	    "# of transactions queued to driver");
1048 	SYSCTL_ADD_INT(ctx, n,
1049 	    OID_AUTO, "out", CTLFLAG_RD,
1050 	    &ios->out, 0,
1051 	    "# of transactions completed (including with error)");
1052 	SYSCTL_ADD_INT(ctx, n,
1053 	    OID_AUTO, "errs", CTLFLAG_RD,
1054 	    &ios->errs, 0,
1055 	    "# of transactions completed with an error");
1056 
1057 	SYSCTL_ADD_PROC(ctx, n,
1058 	    OID_AUTO, "limiter",
1059 	    CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE,
1060 	    ios, 0, cam_iosched_limiter_sysctl, "A",
1061 	    "Current limiting type.");
1062 	SYSCTL_ADD_INT(ctx, n,
1063 	    OID_AUTO, "min", CTLFLAG_RW,
1064 	    &ios->min, 0,
1065 	    "min resource");
1066 	SYSCTL_ADD_INT(ctx, n,
1067 	    OID_AUTO, "max", CTLFLAG_RW,
1068 	    &ios->max, 0,
1069 	    "max resource");
1070 	SYSCTL_ADD_INT(ctx, n,
1071 	    OID_AUTO, "current", CTLFLAG_RW,
1072 	    &ios->current, 0,
1073 	    "current resource");
1074 
1075 	SYSCTL_ADD_PROC(ctx, n,
1076 	    OID_AUTO, "latencies",
1077 	    CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE,
1078 	    &ios->latencies, 0,
1079 	    cam_iosched_sysctl_latencies, "A",
1080 	    "Array of power of 2 latency from 1ms to 1.024s");
1081 }
1082 
1083 static void
1084 cam_iosched_iop_stats_fini(struct iop_stats *ios)
1085 {
1086 	if (ios->sysctl_tree)
1087 		if (sysctl_ctx_free(&ios->sysctl_ctx) != 0)
1088 			printf("can't remove iosched sysctl stats context\n");
1089 }
1090 
1091 static void
1092 cam_iosched_cl_sysctl_init(struct cam_iosched_softc *isc)
1093 {
1094 	struct sysctl_oid_list *n;
1095 	struct sysctl_ctx_list *ctx;
1096 	struct control_loop *clp;
1097 
1098 	clp = &isc->cl;
1099 	clp->sysctl_tree = SYSCTL_ADD_NODE(&isc->sysctl_ctx,
1100 	    SYSCTL_CHILDREN(isc->sysctl_tree), OID_AUTO, "control",
1101 	    CTLFLAG_RD | CTLFLAG_MPSAFE, 0, "Control loop info");
1102 	n = SYSCTL_CHILDREN(clp->sysctl_tree);
1103 	ctx = &clp->sysctl_ctx;
1104 
1105 	SYSCTL_ADD_PROC(ctx, n,
1106 	    OID_AUTO, "type",
1107 	    CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE,
1108 	    clp, 0, cam_iosched_control_type_sysctl, "A",
1109 	    "Control loop algorithm");
1110 	SYSCTL_ADD_PROC(ctx, n,
1111 	    OID_AUTO, "steer_interval",
1112 	    CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE,
1113 	    &clp->steer_interval, 0, cam_iosched_sbintime_sysctl, "A",
1114 	    "How often to steer (in us)");
1115 	SYSCTL_ADD_PROC(ctx, n,
1116 	    OID_AUTO, "lolat",
1117 	    CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE,
1118 	    &clp->lolat, 0, cam_iosched_sbintime_sysctl, "A",
1119 	    "Low water mark for Latency (in us)");
1120 	SYSCTL_ADD_PROC(ctx, n,
1121 	    OID_AUTO, "hilat",
1122 	    CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_MPSAFE,
1123 	    &clp->hilat, 0, cam_iosched_sbintime_sysctl, "A",
1124 	    "Hi water mark for Latency (in us)");
1125 	SYSCTL_ADD_INT(ctx, n,
1126 	    OID_AUTO, "alpha", CTLFLAG_RW,
1127 	    &clp->alpha, 0,
1128 	    "Alpha for PLL (x100) aka gain");
1129 }
1130 
1131 static void
1132 cam_iosched_cl_sysctl_fini(struct control_loop *clp)
1133 {
1134 	if (clp->sysctl_tree)
1135 		if (sysctl_ctx_free(&clp->sysctl_ctx) != 0)
1136 			printf("can't remove iosched sysctl control loop context\n");
1137 }
1138 #endif
1139 
1140 /*
1141  * Allocate the iosched structure. This also insulates callers from knowing
1142  * sizeof struct cam_iosched_softc.
1143  */
1144 int
1145 cam_iosched_init(struct cam_iosched_softc **iscp, struct cam_periph *periph)
1146 {
1147 
1148 	*iscp = malloc(sizeof(**iscp), M_CAMSCHED, M_NOWAIT | M_ZERO);
1149 	if (*iscp == NULL)
1150 		return ENOMEM;
1151 #ifdef CAM_IOSCHED_DYNAMIC
1152 	if (iosched_debug)
1153 		printf("CAM IOSCHEDULER Allocating entry at %p\n", *iscp);
1154 #endif
1155 	(*iscp)->sort_io_queue = -1;
1156 	bioq_init(&(*iscp)->bio_queue);
1157 	bioq_init(&(*iscp)->trim_queue);
1158 #ifdef CAM_IOSCHED_DYNAMIC
1159 	if (do_dynamic_iosched) {
1160 		bioq_init(&(*iscp)->write_queue);
1161 		(*iscp)->read_bias = default_read_bias;
1162 		(*iscp)->current_read_bias = 0;
1163 		(*iscp)->quanta = min(hz, 200);
1164 		cam_iosched_iop_stats_init(*iscp, &(*iscp)->read_stats);
1165 		cam_iosched_iop_stats_init(*iscp, &(*iscp)->write_stats);
1166 		cam_iosched_iop_stats_init(*iscp, &(*iscp)->trim_stats);
1167 		(*iscp)->trim_stats.max = 1;	/* Trims are special: one at a time for now */
1168 		(*iscp)->last_time = sbinuptime();
1169 		callout_init_mtx(&(*iscp)->ticker, cam_periph_mtx(periph), 0);
1170 		(*iscp)->periph = periph;
1171 		cam_iosched_cl_init(&(*iscp)->cl, *iscp);
1172 		callout_reset(&(*iscp)->ticker, hz / (*iscp)->quanta, cam_iosched_ticker, *iscp);
1173 		(*iscp)->flags |= CAM_IOSCHED_FLAG_CALLOUT_ACTIVE;
1174 	}
1175 #endif
1176 
1177 	return 0;
1178 }
1179 
1180 /*
1181  * Reclaim all used resources. This assumes that other folks have
1182  * drained the requests in the hardware. Maybe an unwise assumption.
1183  */
1184 void
1185 cam_iosched_fini(struct cam_iosched_softc *isc)
1186 {
1187 	if (isc) {
1188 		cam_iosched_flush(isc, NULL, ENXIO);
1189 #ifdef CAM_IOSCHED_DYNAMIC
1190 		cam_iosched_iop_stats_fini(&isc->read_stats);
1191 		cam_iosched_iop_stats_fini(&isc->write_stats);
1192 		cam_iosched_iop_stats_fini(&isc->trim_stats);
1193 		cam_iosched_cl_sysctl_fini(&isc->cl);
1194 		if (isc->sysctl_tree)
1195 			if (sysctl_ctx_free(&isc->sysctl_ctx) != 0)
1196 				printf("can't remove iosched sysctl stats context\n");
1197 		if (isc->flags & CAM_IOSCHED_FLAG_CALLOUT_ACTIVE) {
1198 			callout_drain(&isc->ticker);
1199 			isc->flags &= ~ CAM_IOSCHED_FLAG_CALLOUT_ACTIVE;
1200 		}
1201 #endif
1202 		free(isc, M_CAMSCHED);
1203 	}
1204 }
1205 
1206 /*
1207  * After we're sure we're attaching a device, go ahead and add
1208  * hooks for any sysctl we may wish to honor.
1209  */
1210 void cam_iosched_sysctl_init(struct cam_iosched_softc *isc,
1211     struct sysctl_ctx_list *ctx, struct sysctl_oid *node)
1212 {
1213 	struct sysctl_oid_list *n;
1214 
1215 	n = SYSCTL_CHILDREN(node);
1216 	SYSCTL_ADD_INT(ctx, n,
1217 		OID_AUTO, "sort_io_queue", CTLFLAG_RW | CTLFLAG_MPSAFE,
1218 		&isc->sort_io_queue, 0,
1219 		"Sort IO queue to try and optimise disk access patterns");
1220 	SYSCTL_ADD_INT(ctx, n,
1221 	    OID_AUTO, "trim_goal", CTLFLAG_RW,
1222 	    &isc->trim_goal, 0,
1223 	    "Number of trims to try to accumulate before sending to hardware");
1224 	SYSCTL_ADD_INT(ctx, n,
1225 	    OID_AUTO, "trim_ticks", CTLFLAG_RW,
1226 	    &isc->trim_goal, 0,
1227 	    "IO Schedul qaunta to hold back trims for when accumulating");
1228 
1229 #ifdef CAM_IOSCHED_DYNAMIC
1230 	if (!do_dynamic_iosched)
1231 		return;
1232 
1233 	isc->sysctl_tree = SYSCTL_ADD_NODE(&isc->sysctl_ctx,
1234 	    SYSCTL_CHILDREN(node), OID_AUTO, "iosched",
1235 	    CTLFLAG_RD | CTLFLAG_MPSAFE, 0, "I/O scheduler statistics");
1236 	n = SYSCTL_CHILDREN(isc->sysctl_tree);
1237 	ctx = &isc->sysctl_ctx;
1238 
1239 	cam_iosched_iop_stats_sysctl_init(isc, &isc->read_stats, "read");
1240 	cam_iosched_iop_stats_sysctl_init(isc, &isc->write_stats, "write");
1241 	cam_iosched_iop_stats_sysctl_init(isc, &isc->trim_stats, "trim");
1242 	cam_iosched_cl_sysctl_init(isc);
1243 
1244 	SYSCTL_ADD_INT(ctx, n,
1245 	    OID_AUTO, "read_bias", CTLFLAG_RW,
1246 	    &isc->read_bias, default_read_bias,
1247 	    "How biased towards read should we be independent of limits");
1248 
1249 	SYSCTL_ADD_PROC(ctx, n,
1250 	    OID_AUTO, "quanta", CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_MPSAFE,
1251 	    &isc->quanta, 0, cam_iosched_quanta_sysctl, "I",
1252 	    "How many quanta per second do we slice the I/O up into");
1253 
1254 	SYSCTL_ADD_INT(ctx, n,
1255 	    OID_AUTO, "total_ticks", CTLFLAG_RD,
1256 	    &isc->total_ticks, 0,
1257 	    "Total number of ticks we've done");
1258 
1259 	SYSCTL_ADD_INT(ctx, n,
1260 	    OID_AUTO, "load", CTLFLAG_RD,
1261 	    &isc->load, 0,
1262 	    "scaled load average / 100");
1263 
1264 	SYSCTL_ADD_U64(ctx, n,
1265 	    OID_AUTO, "latency_trigger", CTLFLAG_RW,
1266 	    &isc->max_lat, 0,
1267 	    "Latency treshold to trigger callbacks");
1268 #endif
1269 }
1270 
1271 void
1272 cam_iosched_set_latfcn(struct cam_iosched_softc *isc,
1273     cam_iosched_latfcn_t fnp, void *argp)
1274 {
1275 #ifdef CAM_IOSCHED_DYNAMIC
1276 	isc->latfcn = fnp;
1277 	isc->latarg = argp;
1278 #endif
1279 }
1280 
1281 /*
1282  * Client drivers can set two parameters. "goal" is the number of BIO_DELETEs
1283  * that will be queued up before iosched will "release" the trims to the client
1284  * driver to wo with what they will (usually combine as many as possible). If we
1285  * don't get this many, after trim_ticks we'll submit the I/O anyway with
1286  * whatever we have.  We do need an I/O of some kind of to clock the deferred
1287  * trims out to disk. Since we will eventually get a write for the super block
1288  * or something before we shutdown, the trims will complete. To be safe, when a
1289  * BIO_FLUSH is presented to the iosched work queue, we set the ticks time far
1290  * enough in the past so we'll present the BIO_DELETEs to the client driver.
1291  * There might be a race if no BIO_DELETESs were queued, a BIO_FLUSH comes in
1292  * and then a BIO_DELETE is sent down. No know client does this, and there's
1293  * already a race between an ordered BIO_FLUSH and any BIO_DELETEs in flight,
1294  * but no client depends on the ordering being honored.
1295  *
1296  * XXX I'm not sure what the interaction between UFS direct BIOs and the BUF
1297  * flushing on shutdown. I think there's bufs that would be dependent on the BIO
1298  * finishing to write out at least metadata, so we'll be fine. To be safe, keep
1299  * the number of ticks low (less than maybe 10s) to avoid shutdown races.
1300  */
1301 
1302 void
1303 cam_iosched_set_trim_goal(struct cam_iosched_softc *isc, int goal)
1304 {
1305 
1306 	isc->trim_goal = goal;
1307 }
1308 
1309 void
1310 cam_iosched_set_trim_ticks(struct cam_iosched_softc *isc, int trim_ticks)
1311 {
1312 
1313 	isc->trim_ticks = trim_ticks;
1314 }
1315 
1316 /*
1317  * Flush outstanding I/O. Consumers of this library don't know all the
1318  * queues we may keep, so this allows all I/O to be flushed in one
1319  * convenient call.
1320  */
1321 void
1322 cam_iosched_flush(struct cam_iosched_softc *isc, struct devstat *stp, int err)
1323 {
1324 	bioq_flush(&isc->bio_queue, stp, err);
1325 	bioq_flush(&isc->trim_queue, stp, err);
1326 #ifdef CAM_IOSCHED_DYNAMIC
1327 	if (do_dynamic_iosched)
1328 		bioq_flush(&isc->write_queue, stp, err);
1329 #endif
1330 }
1331 
1332 #ifdef CAM_IOSCHED_DYNAMIC
1333 static struct bio *
1334 cam_iosched_get_write(struct cam_iosched_softc *isc)
1335 {
1336 	struct bio *bp;
1337 
1338 	/*
1339 	 * We control the write rate by controlling how many requests we send
1340 	 * down to the drive at any one time. Fewer requests limits the
1341 	 * effects of both starvation when the requests take a while and write
1342 	 * amplification when each request is causing more than one write to
1343 	 * the NAND media. Limiting the queue depth like this will also limit
1344 	 * the write throughput and give and reads that want to compete to
1345 	 * compete unfairly.
1346 	 */
1347 	bp = bioq_first(&isc->write_queue);
1348 	if (bp == NULL) {
1349 		if (iosched_debug > 3)
1350 			printf("No writes present in write_queue\n");
1351 		return NULL;
1352 	}
1353 
1354 	/*
1355 	 * If pending read, prefer that based on current read bias
1356 	 * setting.
1357 	 */
1358 	if (bioq_first(&isc->bio_queue) && isc->current_read_bias) {
1359 		if (iosched_debug)
1360 			printf(
1361 			    "Reads present and current_read_bias is %d queued "
1362 			    "writes %d queued reads %d\n",
1363 			    isc->current_read_bias, isc->write_stats.queued,
1364 			    isc->read_stats.queued);
1365 		isc->current_read_bias--;
1366 		/* We're not limiting writes, per se, just doing reads first */
1367 		return NULL;
1368 	}
1369 
1370 	/*
1371 	 * See if our current limiter allows this I/O.
1372 	 */
1373 	if (cam_iosched_limiter_iop(&isc->write_stats, bp) != 0) {
1374 		if (iosched_debug)
1375 			printf("Can't write because limiter says no.\n");
1376 		isc->write_stats.state_flags |= IOP_RATE_LIMITED;
1377 		return NULL;
1378 	}
1379 
1380 	/*
1381 	 * Let's do this: We've passed all the gates and we're a go
1382 	 * to schedule the I/O in the SIM.
1383 	 */
1384 	isc->current_read_bias = isc->read_bias;
1385 	bioq_remove(&isc->write_queue, bp);
1386 	if (bp->bio_cmd == BIO_WRITE) {
1387 		isc->write_stats.queued--;
1388 		isc->write_stats.total++;
1389 		isc->write_stats.pending++;
1390 	}
1391 	if (iosched_debug > 9)
1392 		printf("HWQ : %p %#x\n", bp, bp->bio_cmd);
1393 	isc->write_stats.state_flags &= ~IOP_RATE_LIMITED;
1394 	return bp;
1395 }
1396 #endif
1397 
1398 /*
1399  * Put back a trim that you weren't able to actually schedule this time.
1400  */
1401 void
1402 cam_iosched_put_back_trim(struct cam_iosched_softc *isc, struct bio *bp)
1403 {
1404 	bioq_insert_head(&isc->trim_queue, bp);
1405 	if (isc->queued_trims == 0)
1406 		isc->last_trim_tick = ticks;
1407 	isc->queued_trims++;
1408 #ifdef CAM_IOSCHED_DYNAMIC
1409 	isc->trim_stats.queued++;
1410 	isc->trim_stats.total--;		/* since we put it back, don't double count */
1411 	isc->trim_stats.pending--;
1412 #endif
1413 }
1414 
1415 /*
1416  * gets the next trim from the trim queue.
1417  *
1418  * Assumes we're called with the periph lock held.  It removes this
1419  * trim from the queue and the device must explicitly reinsert it
1420  * should the need arise.
1421  */
1422 struct bio *
1423 cam_iosched_next_trim(struct cam_iosched_softc *isc)
1424 {
1425 	struct bio *bp;
1426 
1427 	bp  = bioq_first(&isc->trim_queue);
1428 	if (bp == NULL)
1429 		return NULL;
1430 	bioq_remove(&isc->trim_queue, bp);
1431 	isc->queued_trims--;
1432 	isc->last_trim_tick = ticks;	/* Reset the tick timer when we take trims */
1433 #ifdef CAM_IOSCHED_DYNAMIC
1434 	isc->trim_stats.queued--;
1435 	isc->trim_stats.total++;
1436 	isc->trim_stats.pending++;
1437 #endif
1438 	return bp;
1439 }
1440 
1441 /*
1442  * gets an available trim from the trim queue, if there's no trim
1443  * already pending. It removes this trim from the queue and the device
1444  * must explicitly reinsert it should the need arise.
1445  *
1446  * Assumes we're called with the periph lock held.
1447  */
1448 struct bio *
1449 cam_iosched_get_trim(struct cam_iosched_softc *isc)
1450 {
1451 #ifdef CAM_IOSCHED_DYNAMIC
1452 	struct bio *bp;
1453 #endif
1454 
1455 	if (!cam_iosched_has_more_trim(isc))
1456 		return NULL;
1457 #ifdef CAM_IOSCHED_DYNAMIC
1458 	bp  = bioq_first(&isc->trim_queue);
1459 	if (bp == NULL)
1460 		return NULL;
1461 
1462 	/*
1463 	 * If pending read, prefer that based on current read bias setting. The
1464 	 * read bias is shared for both writes and TRIMs, but on TRIMs the bias
1465 	 * is for a combined TRIM not a single TRIM request that's come in.
1466 	 */
1467 	if (do_dynamic_iosched) {
1468 		if (bioq_first(&isc->bio_queue) && isc->current_read_bias) {
1469 			if (iosched_debug)
1470 				printf("Reads present and current_read_bias is %d"
1471 				    " queued trims %d queued reads %d\n",
1472 				    isc->current_read_bias, isc->trim_stats.queued,
1473 				    isc->read_stats.queued);
1474 			isc->current_read_bias--;
1475 			/* We're not limiting TRIMS, per se, just doing reads first */
1476 			return NULL;
1477 		}
1478 		/*
1479 		 * We're going to do a trim, so reset the bias.
1480 		 */
1481 		isc->current_read_bias = isc->read_bias;
1482 	}
1483 
1484 	/*
1485 	 * See if our current limiter allows this I/O. Because we only call this
1486 	 * here, and not in next_trim, the 'bandwidth' limits for trims won't
1487 	 * work, while the iops or max queued limits will work. It's tricky
1488 	 * because we want the limits to be from the perspective of the
1489 	 * "commands sent to the device." To make iops work, we need to check
1490 	 * only here (since we want all the ops we combine to count as one). To
1491 	 * make bw limits work, we'd need to check in next_trim, but that would
1492 	 * have the effect of limiting the iops as seen from the upper layers.
1493 	 */
1494 	if (cam_iosched_limiter_iop(&isc->trim_stats, bp) != 0) {
1495 		if (iosched_debug)
1496 			printf("Can't trim because limiter says no.\n");
1497 		isc->trim_stats.state_flags |= IOP_RATE_LIMITED;
1498 		return NULL;
1499 	}
1500 	isc->current_read_bias = isc->read_bias;
1501 	isc->trim_stats.state_flags &= ~IOP_RATE_LIMITED;
1502 	/* cam_iosched_next_trim below keeps proper book */
1503 #endif
1504 	return cam_iosched_next_trim(isc);
1505 }
1506 
1507 
1508 #ifdef CAM_IOSCHED_DYNAMIC
1509 static struct bio *
1510 bio_next(struct bio *bp)
1511 {
1512 	bp = TAILQ_NEXT(bp, bio_queue);
1513 	/*
1514 	 * After the first commands, the ordered bit terminates
1515 	 * our search because BIO_ORDERED acts like a barrier.
1516 	 */
1517 	if (bp == NULL || bp->bio_flags & BIO_ORDERED)
1518 		return NULL;
1519 	return bp;
1520 }
1521 
1522 static bool
1523 cam_iosched_rate_limited(struct iop_stats *ios)
1524 {
1525 	return ios->state_flags & IOP_RATE_LIMITED;
1526 }
1527 #endif
1528 
1529 /*
1530  * Determine what the next bit of work to do is for the periph. The
1531  * default implementation looks to see if we have trims to do, but no
1532  * trims outstanding. If so, we do that. Otherwise we see if we have
1533  * other work. If we do, then we do that. Otherwise why were we called?
1534  */
1535 struct bio *
1536 cam_iosched_next_bio(struct cam_iosched_softc *isc)
1537 {
1538 	struct bio *bp;
1539 
1540 	/*
1541 	 * See if we have a trim that can be scheduled. We can only send one
1542 	 * at a time down, so this takes that into account.
1543 	 *
1544 	 * XXX newer TRIM commands are queueable. Revisit this when we
1545 	 * implement them.
1546 	 */
1547 	if ((bp = cam_iosched_get_trim(isc)) != NULL)
1548 		return bp;
1549 
1550 #ifdef CAM_IOSCHED_DYNAMIC
1551 	/*
1552 	 * See if we have any pending writes, room in the queue for them,
1553 	 * and no pending reads (unless we've scheduled too many).
1554 	 * if so, those are next.
1555 	 */
1556 	if (do_dynamic_iosched) {
1557 		if ((bp = cam_iosched_get_write(isc)) != NULL)
1558 			return bp;
1559 	}
1560 #endif
1561 	/*
1562 	 * next, see if there's other, normal I/O waiting. If so return that.
1563 	 */
1564 #ifdef CAM_IOSCHED_DYNAMIC
1565 	if (do_dynamic_iosched) {
1566 		for (bp = bioq_first(&isc->bio_queue); bp != NULL;
1567 		     bp = bio_next(bp)) {
1568 			/*
1569 			 * For the dynamic scheduler with a read bias, bio_queue
1570 			 * is only for reads. However, without one, all
1571 			 * operations are queued. Enforce limits here for any
1572 			 * operation we find here.
1573 			 */
1574 			if (bp->bio_cmd == BIO_READ) {
1575 				if (cam_iosched_rate_limited(&isc->read_stats) ||
1576 				    cam_iosched_limiter_iop(&isc->read_stats, bp) != 0) {
1577 					isc->read_stats.state_flags |= IOP_RATE_LIMITED;
1578 					continue;
1579 				}
1580 				isc->read_stats.state_flags &= ~IOP_RATE_LIMITED;
1581 			}
1582 			/*
1583 			 * There can only be write requests on the queue when
1584 			 * the read bias is 0, but we need to process them
1585 			 * here. We do not assert for read bias == 0, however,
1586 			 * since it is dynamic and we can have WRITE operations
1587 			 * in the queue after we transition from 0 to non-zero.
1588 			 */
1589 			if (bp->bio_cmd == BIO_WRITE) {
1590 				if (cam_iosched_rate_limited(&isc->write_stats) ||
1591 				    cam_iosched_limiter_iop(&isc->write_stats, bp) != 0) {
1592 					isc->write_stats.state_flags |= IOP_RATE_LIMITED;
1593 					continue;
1594 				}
1595 				isc->write_stats.state_flags &= ~IOP_RATE_LIMITED;
1596 			}
1597 			/*
1598 			 * here we know we have a bp that's != NULL, that's not rate limited
1599 			 * and can be the next I/O.
1600 			 */
1601 			break;
1602 		}
1603 	} else
1604 #endif
1605 		bp = bioq_first(&isc->bio_queue);
1606 
1607 	if (bp == NULL)
1608 		return (NULL);
1609 	bioq_remove(&isc->bio_queue, bp);
1610 #ifdef CAM_IOSCHED_DYNAMIC
1611 	if (do_dynamic_iosched) {
1612 		if (bp->bio_cmd == BIO_READ) {
1613 			isc->read_stats.queued--;
1614 			isc->read_stats.total++;
1615 			isc->read_stats.pending++;
1616 		} else if (bp->bio_cmd == BIO_WRITE) {
1617 			isc->write_stats.queued--;
1618 			isc->write_stats.total++;
1619 			isc->write_stats.pending++;
1620 		}
1621 	}
1622 	if (iosched_debug > 9)
1623 		printf("HWQ : %p %#x\n", bp, bp->bio_cmd);
1624 #endif
1625 	return bp;
1626 }
1627 
1628 /*
1629  * Driver has been given some work to do by the block layer. Tell the
1630  * scheduler about it and have it queue the work up. The scheduler module
1631  * will then return the currently most useful bit of work later, possibly
1632  * deferring work for various reasons.
1633  */
1634 void
1635 cam_iosched_queue_work(struct cam_iosched_softc *isc, struct bio *bp)
1636 {
1637 
1638 	/*
1639 	 * A BIO_SPEEDUP from the uppper layers means that they have a block
1640 	 * shortage. At the present, this is only sent when we're trying to
1641 	 * allocate blocks, but have a shortage before giving up. bio_length is
1642 	 * the size of their shortage. We will complete just enough BIO_DELETEs
1643 	 * in the queue to satisfy the need. If bio_length is 0, we'll complete
1644 	 * them all. This allows the scheduler to delay BIO_DELETEs to improve
1645 	 * read/write performance without worrying about the upper layers. When
1646 	 * it's possibly a problem, we respond by pretending the BIO_DELETEs
1647 	 * just worked. We can't do anything about the BIO_DELETEs in the
1648 	 * hardware, though. We have to wait for them to complete.
1649 	 */
1650 	if (bp->bio_cmd == BIO_SPEEDUP) {
1651 		off_t len;
1652 		struct bio *nbp;
1653 
1654 		len = 0;
1655 		while (bioq_first(&isc->trim_queue) &&
1656 		    (bp->bio_length == 0 || len < bp->bio_length)) {
1657 			nbp = bioq_takefirst(&isc->trim_queue);
1658 			len += nbp->bio_length;
1659 			nbp->bio_error = 0;
1660 			biodone(nbp);
1661 		}
1662 		if (bp->bio_length > 0) {
1663 			if (bp->bio_length > len)
1664 				bp->bio_resid = bp->bio_length - len;
1665 			else
1666 				bp->bio_resid = 0;
1667 		}
1668 		bp->bio_error = 0;
1669 		biodone(bp);
1670 		return;
1671 	}
1672 
1673 	/*
1674 	 * If we get a BIO_FLUSH, and we're doing delayed BIO_DELETEs then we
1675 	 * set the last tick time to one less than the current ticks minus the
1676 	 * delay to force the BIO_DELETEs to be presented to the client driver.
1677 	 */
1678 	if (bp->bio_cmd == BIO_FLUSH && isc->trim_ticks > 0)
1679 		isc->last_trim_tick = ticks - isc->trim_ticks - 1;
1680 
1681 	/*
1682 	 * Put all trims on the trim queue. Otherwise put the work on the bio
1683 	 * queue.
1684 	 */
1685 	if (bp->bio_cmd == BIO_DELETE) {
1686 		bioq_insert_tail(&isc->trim_queue, bp);
1687 		if (isc->queued_trims == 0)
1688 			isc->last_trim_tick = ticks;
1689 		isc->queued_trims++;
1690 #ifdef CAM_IOSCHED_DYNAMIC
1691 		isc->trim_stats.in++;
1692 		isc->trim_stats.queued++;
1693 #endif
1694 	}
1695 #ifdef CAM_IOSCHED_DYNAMIC
1696 	else if (do_dynamic_iosched && isc->read_bias != 0 &&
1697 	    (bp->bio_cmd != BIO_READ)) {
1698 		if (cam_iosched_sort_queue(isc))
1699 			bioq_disksort(&isc->write_queue, bp);
1700 		else
1701 			bioq_insert_tail(&isc->write_queue, bp);
1702 		if (iosched_debug > 9)
1703 			printf("Qw  : %p %#x\n", bp, bp->bio_cmd);
1704 		if (bp->bio_cmd == BIO_WRITE) {
1705 			isc->write_stats.in++;
1706 			isc->write_stats.queued++;
1707 		}
1708 	}
1709 #endif
1710 	else {
1711 		if (cam_iosched_sort_queue(isc))
1712 			bioq_disksort(&isc->bio_queue, bp);
1713 		else
1714 			bioq_insert_tail(&isc->bio_queue, bp);
1715 #ifdef CAM_IOSCHED_DYNAMIC
1716 		if (iosched_debug > 9)
1717 			printf("Qr  : %p %#x\n", bp, bp->bio_cmd);
1718 		if (bp->bio_cmd == BIO_READ) {
1719 			isc->read_stats.in++;
1720 			isc->read_stats.queued++;
1721 		} else if (bp->bio_cmd == BIO_WRITE) {
1722 			isc->write_stats.in++;
1723 			isc->write_stats.queued++;
1724 		}
1725 #endif
1726 	}
1727 }
1728 
1729 /*
1730  * If we have work, get it scheduled. Called with the periph lock held.
1731  */
1732 void
1733 cam_iosched_schedule(struct cam_iosched_softc *isc, struct cam_periph *periph)
1734 {
1735 
1736 	if (cam_iosched_has_work(isc))
1737 		xpt_schedule(periph, CAM_PRIORITY_NORMAL);
1738 }
1739 
1740 /*
1741  * Complete a trim request. Mark that we no longer have one in flight.
1742  */
1743 void
1744 cam_iosched_trim_done(struct cam_iosched_softc *isc)
1745 {
1746 
1747 	isc->flags &= ~CAM_IOSCHED_FLAG_TRIM_ACTIVE;
1748 }
1749 
1750 /*
1751  * Complete a bio. Called before we release the ccb with xpt_release_ccb so we
1752  * might use notes in the ccb for statistics.
1753  */
1754 int
1755 cam_iosched_bio_complete(struct cam_iosched_softc *isc, struct bio *bp,
1756     union ccb *done_ccb)
1757 {
1758 	int retval = 0;
1759 #ifdef CAM_IOSCHED_DYNAMIC
1760 	if (!do_dynamic_iosched)
1761 		return retval;
1762 
1763 	if (iosched_debug > 10)
1764 		printf("done: %p %#x\n", bp, bp->bio_cmd);
1765 	if (bp->bio_cmd == BIO_WRITE) {
1766 		retval = cam_iosched_limiter_iodone(&isc->write_stats, bp);
1767 		if ((bp->bio_flags & BIO_ERROR) != 0)
1768 			isc->write_stats.errs++;
1769 		isc->write_stats.out++;
1770 		isc->write_stats.pending--;
1771 	} else if (bp->bio_cmd == BIO_READ) {
1772 		retval = cam_iosched_limiter_iodone(&isc->read_stats, bp);
1773 		if ((bp->bio_flags & BIO_ERROR) != 0)
1774 			isc->read_stats.errs++;
1775 		isc->read_stats.out++;
1776 		isc->read_stats.pending--;
1777 	} else if (bp->bio_cmd == BIO_DELETE) {
1778 		if ((bp->bio_flags & BIO_ERROR) != 0)
1779 			isc->trim_stats.errs++;
1780 		isc->trim_stats.out++;
1781 		isc->trim_stats.pending--;
1782 	} else if (bp->bio_cmd != BIO_FLUSH) {
1783 		if (iosched_debug)
1784 			printf("Completing command with bio_cmd == %#x\n", bp->bio_cmd);
1785 	}
1786 
1787 	if ((bp->bio_flags & BIO_ERROR) == 0 && done_ccb != NULL &&
1788 	    (done_ccb->ccb_h.status & CAM_QOS_VALID) != 0) {
1789 		sbintime_t sim_latency;
1790 
1791 		sim_latency = cam_iosched_sbintime_t(done_ccb->ccb_h.qos.periph_data);
1792 
1793 		cam_iosched_io_metric_update(isc, sim_latency,
1794 		    bp->bio_cmd, bp->bio_bcount);
1795 		/*
1796 		 * Debugging code: allow callbacks to the periph driver when latency max
1797 		 * is exceeded. This can be useful for triggering external debugging actions.
1798 		 */
1799 		if (isc->latfcn && isc->max_lat != 0 && sim_latency > isc->max_lat)
1800 			isc->latfcn(isc->latarg, sim_latency, bp);
1801 	}
1802 
1803 #endif
1804 	return retval;
1805 }
1806 
1807 /*
1808  * Tell the io scheduler that you've pushed a trim down into the sim.
1809  * This also tells the I/O scheduler not to push any more trims down, so
1810  * some periphs do not call it if they can cope with multiple trims in flight.
1811  */
1812 void
1813 cam_iosched_submit_trim(struct cam_iosched_softc *isc)
1814 {
1815 
1816 	isc->flags |= CAM_IOSCHED_FLAG_TRIM_ACTIVE;
1817 }
1818 
1819 /*
1820  * Change the sorting policy hint for I/O transactions for this device.
1821  */
1822 void
1823 cam_iosched_set_sort_queue(struct cam_iosched_softc *isc, int val)
1824 {
1825 
1826 	isc->sort_io_queue = val;
1827 }
1828 
1829 int
1830 cam_iosched_has_work_flags(struct cam_iosched_softc *isc, uint32_t flags)
1831 {
1832 	return isc->flags & flags;
1833 }
1834 
1835 void
1836 cam_iosched_set_work_flags(struct cam_iosched_softc *isc, uint32_t flags)
1837 {
1838 	isc->flags |= flags;
1839 }
1840 
1841 void
1842 cam_iosched_clr_work_flags(struct cam_iosched_softc *isc, uint32_t flags)
1843 {
1844 	isc->flags &= ~flags;
1845 }
1846 
1847 #ifdef CAM_IOSCHED_DYNAMIC
1848 /*
1849  * After the method presented in Jack Crenshaw's 1998 article "Integer
1850  * Square Roots," reprinted at
1851  * http://www.embedded.com/electronics-blogs/programmer-s-toolbox/4219659/Integer-Square-Roots
1852  * and well worth the read. Briefly, we find the power of 4 that's the
1853  * largest smaller than val. We then check each smaller power of 4 to
1854  * see if val is still bigger. The right shifts at each step divide
1855  * the result by 2 which after successive application winds up
1856  * accumulating the right answer. It could also have been accumulated
1857  * using a separate root counter, but this code is smaller and faster
1858  * than that method. This method is also integer size invariant.
1859  * It returns floor(sqrt((float)val)), or the largest integer less than
1860  * or equal to the square root.
1861  */
1862 static uint64_t
1863 isqrt64(uint64_t val)
1864 {
1865 	uint64_t res = 0;
1866 	uint64_t bit = 1ULL << (sizeof(uint64_t) * NBBY - 2);
1867 
1868 	/*
1869 	 * Find the largest power of 4 smaller than val.
1870 	 */
1871 	while (bit > val)
1872 		bit >>= 2;
1873 
1874 	/*
1875 	 * Accumulate the answer, one bit at a time (we keep moving
1876 	 * them over since 2 is the square root of 4 and we test
1877 	 * powers of 4). We accumulate where we find the bit, but
1878 	 * the successive shifts land the bit in the right place
1879 	 * by the end.
1880 	 */
1881 	while (bit != 0) {
1882 		if (val >= res + bit) {
1883 			val -= res + bit;
1884 			res = (res >> 1) + bit;
1885 		} else
1886 			res >>= 1;
1887 		bit >>= 2;
1888 	}
1889 
1890 	return res;
1891 }
1892 
1893 static sbintime_t latencies[LAT_BUCKETS - 1] = {
1894 	BUCKET_BASE <<  0,	/* 20us */
1895 	BUCKET_BASE <<  1,
1896 	BUCKET_BASE <<  2,
1897 	BUCKET_BASE <<  3,
1898 	BUCKET_BASE <<  4,
1899 	BUCKET_BASE <<  5,
1900 	BUCKET_BASE <<  6,
1901 	BUCKET_BASE <<  7,
1902 	BUCKET_BASE <<  8,
1903 	BUCKET_BASE <<  9,
1904 	BUCKET_BASE << 10,
1905 	BUCKET_BASE << 11,
1906 	BUCKET_BASE << 12,
1907 	BUCKET_BASE << 13,
1908 	BUCKET_BASE << 14,
1909 	BUCKET_BASE << 15,
1910 	BUCKET_BASE << 16,
1911 	BUCKET_BASE << 17,
1912 	BUCKET_BASE << 18	/* 5,242,880us */
1913 };
1914 
1915 static void
1916 cam_iosched_update(struct iop_stats *iop, sbintime_t sim_latency)
1917 {
1918 	sbintime_t y, deltasq, delta;
1919 	int i;
1920 
1921 	/*
1922 	 * Keep counts for latency. We do it by power of two buckets.
1923 	 * This helps us spot outlier behavior obscured by averages.
1924 	 */
1925 	for (i = 0; i < LAT_BUCKETS - 1; i++) {
1926 		if (sim_latency < latencies[i]) {
1927 			iop->latencies[i]++;
1928 			break;
1929 		}
1930 	}
1931 	if (i == LAT_BUCKETS - 1)
1932 		iop->latencies[i]++; 	 /* Put all > 8192ms values into the last bucket. */
1933 
1934 	/*
1935 	 * Classic exponentially decaying average with a tiny alpha
1936 	 * (2 ^ -alpha_bits). For more info see the NIST statistical
1937 	 * handbook.
1938 	 *
1939 	 * ema_t = y_t * alpha + ema_t-1 * (1 - alpha)		[nist]
1940 	 * ema_t = y_t * alpha + ema_t-1 - alpha * ema_t-1
1941 	 * ema_t = alpha * y_t - alpha * ema_t-1 + ema_t-1
1942 	 * alpha = 1 / (1 << alpha_bits)
1943 	 * sub e == ema_t-1, b == 1/alpha (== 1 << alpha_bits), d == y_t - ema_t-1
1944 	 *	= y_t/b - e/b + be/b
1945 	 *      = (y_t - e + be) / b
1946 	 *	= (e + d) / b
1947 	 *
1948 	 * Since alpha is a power of two, we can compute this w/o any mult or
1949 	 * division.
1950 	 *
1951 	 * Variance can also be computed. Usually, it would be expressed as follows:
1952 	 *	diff_t = y_t - ema_t-1
1953 	 *	emvar_t = (1 - alpha) * (emavar_t-1 + diff_t^2 * alpha)
1954 	 *	  = emavar_t-1 - alpha * emavar_t-1 + delta_t^2 * alpha - (delta_t * alpha)^2
1955 	 * sub b == 1/alpha (== 1 << alpha_bits), e == emavar_t-1, d = delta_t^2
1956 	 *	  = e - e/b + dd/b + dd/bb
1957 	 *	  = (bbe - be + bdd + dd) / bb
1958 	 *	  = (bbe + b(dd-e) + dd) / bb (which is expanded below bb = 1<<(2*alpha_bits))
1959 	 */
1960 	/*
1961 	 * XXX possible numeric issues
1962 	 *	o We assume right shifted integers do the right thing, since that's
1963 	 *	  implementation defined. You can change the right shifts to / (1LL << alpha).
1964 	 *	o alpha_bits = 9 gives ema ceiling of 23 bits of seconds for ema and 14 bits
1965 	 *	  for emvar. This puts a ceiling of 13 bits on alpha since we need a
1966 	 *	  few tens of seconds of representation.
1967 	 *	o We mitigate alpha issues by never setting it too high.
1968 	 */
1969 	y = sim_latency;
1970 	delta = (y - iop->ema);					/* d */
1971 	iop->ema = ((iop->ema << alpha_bits) + delta) >> alpha_bits;
1972 
1973 	/*
1974 	 * Were we to naively plow ahead at this point, we wind up with many numerical
1975 	 * issues making any SD > ~3ms unreliable. So, we shift right by 12. This leaves
1976 	 * us with microsecond level precision in the input, so the same in the
1977 	 * output. It means we can't overflow deltasq unless delta > 4k seconds. It
1978 	 * also means that emvar can be up 46 bits 40 of which are fraction, which
1979 	 * gives us a way to measure up to ~8s in the SD before the computation goes
1980 	 * unstable. Even the worst hard disk rarely has > 1s service time in the
1981 	 * drive. It does mean we have to shift left 12 bits after taking the
1982 	 * square root to compute the actual standard deviation estimate. This loss of
1983 	 * precision is preferable to needing int128 types to work. The above numbers
1984 	 * assume alpha=9. 10 or 11 are ok, but we start to run into issues at 12,
1985 	 * so 12 or 13 is OK for EMA, EMVAR and SD will be wrong in those cases.
1986 	 */
1987 	delta >>= 12;
1988 	deltasq = delta * delta;				/* dd */
1989 	iop->emvar = ((iop->emvar << (2 * alpha_bits)) +	/* bbe */
1990 	    ((deltasq - iop->emvar) << alpha_bits) +		/* b(dd-e) */
1991 	    deltasq)						/* dd */
1992 	    >> (2 * alpha_bits);				/* div bb */
1993 	iop->sd = (sbintime_t)isqrt64((uint64_t)iop->emvar) << 12;
1994 }
1995 
1996 static void
1997 cam_iosched_io_metric_update(struct cam_iosched_softc *isc,
1998     sbintime_t sim_latency, int cmd, size_t size)
1999 {
2000 	/* xxx Do we need to scale based on the size of the I/O ? */
2001 	switch (cmd) {
2002 	case BIO_READ:
2003 		cam_iosched_update(&isc->read_stats, sim_latency);
2004 		break;
2005 	case BIO_WRITE:
2006 		cam_iosched_update(&isc->write_stats, sim_latency);
2007 		break;
2008 	case BIO_DELETE:
2009 		cam_iosched_update(&isc->trim_stats, sim_latency);
2010 		break;
2011 	default:
2012 		break;
2013 	}
2014 }
2015 
2016 #ifdef DDB
2017 static int biolen(struct bio_queue_head *bq)
2018 {
2019 	int i = 0;
2020 	struct bio *bp;
2021 
2022 	TAILQ_FOREACH(bp, &bq->queue, bio_queue) {
2023 		i++;
2024 	}
2025 	return i;
2026 }
2027 
2028 /*
2029  * Show the internal state of the I/O scheduler.
2030  */
2031 DB_SHOW_COMMAND(iosched, cam_iosched_db_show)
2032 {
2033 	struct cam_iosched_softc *isc;
2034 
2035 	if (!have_addr) {
2036 		db_printf("Need addr\n");
2037 		return;
2038 	}
2039 	isc = (struct cam_iosched_softc *)addr;
2040 	db_printf("pending_reads:     %d\n", isc->read_stats.pending);
2041 	db_printf("min_reads:         %d\n", isc->read_stats.min);
2042 	db_printf("max_reads:         %d\n", isc->read_stats.max);
2043 	db_printf("reads:             %d\n", isc->read_stats.total);
2044 	db_printf("in_reads:          %d\n", isc->read_stats.in);
2045 	db_printf("out_reads:         %d\n", isc->read_stats.out);
2046 	db_printf("queued_reads:      %d\n", isc->read_stats.queued);
2047 	db_printf("Read Q len         %d\n", biolen(&isc->bio_queue));
2048 	db_printf("pending_writes:    %d\n", isc->write_stats.pending);
2049 	db_printf("min_writes:        %d\n", isc->write_stats.min);
2050 	db_printf("max_writes:        %d\n", isc->write_stats.max);
2051 	db_printf("writes:            %d\n", isc->write_stats.total);
2052 	db_printf("in_writes:         %d\n", isc->write_stats.in);
2053 	db_printf("out_writes:        %d\n", isc->write_stats.out);
2054 	db_printf("queued_writes:     %d\n", isc->write_stats.queued);
2055 	db_printf("Write Q len        %d\n", biolen(&isc->write_queue));
2056 	db_printf("pending_trims:     %d\n", isc->trim_stats.pending);
2057 	db_printf("min_trims:         %d\n", isc->trim_stats.min);
2058 	db_printf("max_trims:         %d\n", isc->trim_stats.max);
2059 	db_printf("trims:             %d\n", isc->trim_stats.total);
2060 	db_printf("in_trims:          %d\n", isc->trim_stats.in);
2061 	db_printf("out_trims:         %d\n", isc->trim_stats.out);
2062 	db_printf("queued_trims:      %d\n", isc->trim_stats.queued);
2063 	db_printf("Trim Q len         %d\n", biolen(&isc->trim_queue));
2064 	db_printf("read_bias:         %d\n", isc->read_bias);
2065 	db_printf("current_read_bias: %d\n", isc->current_read_bias);
2066 	db_printf("Trim active?       %s\n",
2067 	    (isc->flags & CAM_IOSCHED_FLAG_TRIM_ACTIVE) ? "yes" : "no");
2068 }
2069 #endif
2070 #endif
2071