1 /* 2 * latencytop.c: Latency display infrastructure 3 * 4 * (C) Copyright 2008 Intel Corporation 5 * Author: Arjan van de Ven <arjan@linux.intel.com> 6 * 7 * This program is free software; you can redistribute it and/or 8 * modify it under the terms of the GNU General Public License 9 * as published by the Free Software Foundation; version 2 10 * of the License. 11 */ 12 13 /* 14 * CONFIG_LATENCYTOP enables a kernel latency tracking infrastructure that is 15 * used by the "latencytop" userspace tool. The latency that is tracked is not 16 * the 'traditional' interrupt latency (which is primarily caused by something 17 * else consuming CPU), but instead, it is the latency an application encounters 18 * because the kernel sleeps on its behalf for various reasons. 19 * 20 * This code tracks 2 levels of statistics: 21 * 1) System level latency 22 * 2) Per process latency 23 * 24 * The latency is stored in fixed sized data structures in an accumulated form; 25 * if the "same" latency cause is hit twice, this will be tracked as one entry 26 * in the data structure. Both the count, total accumulated latency and maximum 27 * latency are tracked in this data structure. When the fixed size structure is 28 * full, no new causes are tracked until the buffer is flushed by writing to 29 * the /proc file; the userspace tool does this on a regular basis. 30 * 31 * A latency cause is identified by a stringified backtrace at the point that 32 * the scheduler gets invoked. The userland tool will use this string to 33 * identify the cause of the latency in human readable form. 34 * 35 * The information is exported via /proc/latency_stats and /proc/<pid>/latency. 36 * These files look like this: 37 * 38 * Latency Top version : v0.1 39 * 70 59433 4897 i915_irq_wait drm_ioctl vfs_ioctl do_vfs_ioctl sys_ioctl 40 * | | | | 41 * | | | +----> the stringified backtrace 42 * | | +---------> The maximum latency for this entry in microseconds 43 * | +--------------> The accumulated latency for this entry (microseconds) 44 * +-------------------> The number of times this entry is hit 45 * 46 * (note: the average latency is the accumulated latency divided by the number 47 * of times) 48 */ 49 50 #include <linux/kallsyms.h> 51 #include <linux/seq_file.h> 52 #include <linux/notifier.h> 53 #include <linux/spinlock.h> 54 #include <linux/proc_fs.h> 55 #include <linux/latencytop.h> 56 #include <linux/export.h> 57 #include <linux/sched.h> 58 #include <linux/list.h> 59 #include <linux/stacktrace.h> 60 61 static DEFINE_RAW_SPINLOCK(latency_lock); 62 63 #define MAXLR 128 64 static struct latency_record latency_record[MAXLR]; 65 66 int latencytop_enabled; 67 68 void clear_all_latency_tracing(struct task_struct *p) 69 { 70 unsigned long flags; 71 72 if (!latencytop_enabled) 73 return; 74 75 raw_spin_lock_irqsave(&latency_lock, flags); 76 memset(&p->latency_record, 0, sizeof(p->latency_record)); 77 p->latency_record_count = 0; 78 raw_spin_unlock_irqrestore(&latency_lock, flags); 79 } 80 81 static void clear_global_latency_tracing(void) 82 { 83 unsigned long flags; 84 85 raw_spin_lock_irqsave(&latency_lock, flags); 86 memset(&latency_record, 0, sizeof(latency_record)); 87 raw_spin_unlock_irqrestore(&latency_lock, flags); 88 } 89 90 static void __sched 91 account_global_scheduler_latency(struct task_struct *tsk, 92 struct latency_record *lat) 93 { 94 int firstnonnull = MAXLR + 1; 95 int i; 96 97 if (!latencytop_enabled) 98 return; 99 100 /* skip kernel threads for now */ 101 if (!tsk->mm) 102 return; 103 104 for (i = 0; i < MAXLR; i++) { 105 int q, same = 1; 106 107 /* Nothing stored: */ 108 if (!latency_record[i].backtrace[0]) { 109 if (firstnonnull > i) 110 firstnonnull = i; 111 continue; 112 } 113 for (q = 0; q < LT_BACKTRACEDEPTH; q++) { 114 unsigned long record = lat->backtrace[q]; 115 116 if (latency_record[i].backtrace[q] != record) { 117 same = 0; 118 break; 119 } 120 121 /* 0 and ULONG_MAX entries mean end of backtrace: */ 122 if (record == 0 || record == ULONG_MAX) 123 break; 124 } 125 if (same) { 126 latency_record[i].count++; 127 latency_record[i].time += lat->time; 128 if (lat->time > latency_record[i].max) 129 latency_record[i].max = lat->time; 130 return; 131 } 132 } 133 134 i = firstnonnull; 135 if (i >= MAXLR - 1) 136 return; 137 138 /* Allocted a new one: */ 139 memcpy(&latency_record[i], lat, sizeof(struct latency_record)); 140 } 141 142 /* 143 * Iterator to store a backtrace into a latency record entry 144 */ 145 static inline void store_stacktrace(struct task_struct *tsk, 146 struct latency_record *lat) 147 { 148 struct stack_trace trace; 149 150 memset(&trace, 0, sizeof(trace)); 151 trace.max_entries = LT_BACKTRACEDEPTH; 152 trace.entries = &lat->backtrace[0]; 153 save_stack_trace_tsk(tsk, &trace); 154 } 155 156 /** 157 * __account_scheduler_latency - record an occurred latency 158 * @tsk - the task struct of the task hitting the latency 159 * @usecs - the duration of the latency in microseconds 160 * @inter - 1 if the sleep was interruptible, 0 if uninterruptible 161 * 162 * This function is the main entry point for recording latency entries 163 * as called by the scheduler. 164 * 165 * This function has a few special cases to deal with normal 'non-latency' 166 * sleeps: specifically, interruptible sleep longer than 5 msec is skipped 167 * since this usually is caused by waiting for events via select() and co. 168 * 169 * Negative latencies (caused by time going backwards) are also explicitly 170 * skipped. 171 */ 172 void __sched 173 __account_scheduler_latency(struct task_struct *tsk, int usecs, int inter) 174 { 175 unsigned long flags; 176 int i, q; 177 struct latency_record lat; 178 179 /* Long interruptible waits are generally user requested... */ 180 if (inter && usecs > 5000) 181 return; 182 183 /* Negative sleeps are time going backwards */ 184 /* Zero-time sleeps are non-interesting */ 185 if (usecs <= 0) 186 return; 187 188 memset(&lat, 0, sizeof(lat)); 189 lat.count = 1; 190 lat.time = usecs; 191 lat.max = usecs; 192 store_stacktrace(tsk, &lat); 193 194 raw_spin_lock_irqsave(&latency_lock, flags); 195 196 account_global_scheduler_latency(tsk, &lat); 197 198 for (i = 0; i < tsk->latency_record_count; i++) { 199 struct latency_record *mylat; 200 int same = 1; 201 202 mylat = &tsk->latency_record[i]; 203 for (q = 0; q < LT_BACKTRACEDEPTH; q++) { 204 unsigned long record = lat.backtrace[q]; 205 206 if (mylat->backtrace[q] != record) { 207 same = 0; 208 break; 209 } 210 211 /* 0 and ULONG_MAX entries mean end of backtrace: */ 212 if (record == 0 || record == ULONG_MAX) 213 break; 214 } 215 if (same) { 216 mylat->count++; 217 mylat->time += lat.time; 218 if (lat.time > mylat->max) 219 mylat->max = lat.time; 220 goto out_unlock; 221 } 222 } 223 224 /* 225 * short term hack; if we're > 32 we stop; future we recycle: 226 */ 227 if (tsk->latency_record_count >= LT_SAVECOUNT) 228 goto out_unlock; 229 230 /* Allocated a new one: */ 231 i = tsk->latency_record_count++; 232 memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record)); 233 234 out_unlock: 235 raw_spin_unlock_irqrestore(&latency_lock, flags); 236 } 237 238 static int lstats_show(struct seq_file *m, void *v) 239 { 240 int i; 241 242 seq_puts(m, "Latency Top version : v0.1\n"); 243 244 for (i = 0; i < MAXLR; i++) { 245 struct latency_record *lr = &latency_record[i]; 246 247 if (lr->backtrace[0]) { 248 int q; 249 seq_printf(m, "%i %lu %lu", 250 lr->count, lr->time, lr->max); 251 for (q = 0; q < LT_BACKTRACEDEPTH; q++) { 252 unsigned long bt = lr->backtrace[q]; 253 if (!bt) 254 break; 255 if (bt == ULONG_MAX) 256 break; 257 seq_printf(m, " %ps", (void *)bt); 258 } 259 seq_puts(m, "\n"); 260 } 261 } 262 return 0; 263 } 264 265 static ssize_t 266 lstats_write(struct file *file, const char __user *buf, size_t count, 267 loff_t *offs) 268 { 269 clear_global_latency_tracing(); 270 271 return count; 272 } 273 274 static int lstats_open(struct inode *inode, struct file *filp) 275 { 276 return single_open(filp, lstats_show, NULL); 277 } 278 279 static const struct file_operations lstats_fops = { 280 .open = lstats_open, 281 .read = seq_read, 282 .write = lstats_write, 283 .llseek = seq_lseek, 284 .release = single_release, 285 }; 286 287 static int __init init_lstats_procfs(void) 288 { 289 proc_create("latency_stats", 0644, NULL, &lstats_fops); 290 return 0; 291 } 292 293 int sysctl_latencytop(struct ctl_table *table, int write, 294 void __user *buffer, size_t *lenp, loff_t *ppos) 295 { 296 int err; 297 298 err = proc_dointvec(table, write, buffer, lenp, ppos); 299 if (latencytop_enabled) 300 force_schedstat_enabled(); 301 302 return err; 303 } 304 device_initcall(init_lstats_procfs); 305