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/sched/debug.h> 59 #include <linux/sched/stat.h> 60 #include <linux/list.h> 61 #include <linux/stacktrace.h> 62 63 static DEFINE_RAW_SPINLOCK(latency_lock); 64 65 #define MAXLR 128 66 static struct latency_record latency_record[MAXLR]; 67 68 int latencytop_enabled; 69 70 void clear_all_latency_tracing(struct task_struct *p) 71 { 72 unsigned long flags; 73 74 if (!latencytop_enabled) 75 return; 76 77 raw_spin_lock_irqsave(&latency_lock, flags); 78 memset(&p->latency_record, 0, sizeof(p->latency_record)); 79 p->latency_record_count = 0; 80 raw_spin_unlock_irqrestore(&latency_lock, flags); 81 } 82 83 static void clear_global_latency_tracing(void) 84 { 85 unsigned long flags; 86 87 raw_spin_lock_irqsave(&latency_lock, flags); 88 memset(&latency_record, 0, sizeof(latency_record)); 89 raw_spin_unlock_irqrestore(&latency_lock, flags); 90 } 91 92 static void __sched 93 account_global_scheduler_latency(struct task_struct *tsk, 94 struct latency_record *lat) 95 { 96 int firstnonnull = MAXLR + 1; 97 int i; 98 99 if (!latencytop_enabled) 100 return; 101 102 /* skip kernel threads for now */ 103 if (!tsk->mm) 104 return; 105 106 for (i = 0; i < MAXLR; i++) { 107 int q, same = 1; 108 109 /* Nothing stored: */ 110 if (!latency_record[i].backtrace[0]) { 111 if (firstnonnull > i) 112 firstnonnull = i; 113 continue; 114 } 115 for (q = 0; q < LT_BACKTRACEDEPTH; q++) { 116 unsigned long record = lat->backtrace[q]; 117 118 if (latency_record[i].backtrace[q] != record) { 119 same = 0; 120 break; 121 } 122 123 /* 0 and ULONG_MAX entries mean end of backtrace: */ 124 if (record == 0 || record == ULONG_MAX) 125 break; 126 } 127 if (same) { 128 latency_record[i].count++; 129 latency_record[i].time += lat->time; 130 if (lat->time > latency_record[i].max) 131 latency_record[i].max = lat->time; 132 return; 133 } 134 } 135 136 i = firstnonnull; 137 if (i >= MAXLR - 1) 138 return; 139 140 /* Allocted a new one: */ 141 memcpy(&latency_record[i], lat, sizeof(struct latency_record)); 142 } 143 144 /* 145 * Iterator to store a backtrace into a latency record entry 146 */ 147 static inline void store_stacktrace(struct task_struct *tsk, 148 struct latency_record *lat) 149 { 150 struct stack_trace trace; 151 152 memset(&trace, 0, sizeof(trace)); 153 trace.max_entries = LT_BACKTRACEDEPTH; 154 trace.entries = &lat->backtrace[0]; 155 save_stack_trace_tsk(tsk, &trace); 156 } 157 158 /** 159 * __account_scheduler_latency - record an occurred latency 160 * @tsk - the task struct of the task hitting the latency 161 * @usecs - the duration of the latency in microseconds 162 * @inter - 1 if the sleep was interruptible, 0 if uninterruptible 163 * 164 * This function is the main entry point for recording latency entries 165 * as called by the scheduler. 166 * 167 * This function has a few special cases to deal with normal 'non-latency' 168 * sleeps: specifically, interruptible sleep longer than 5 msec is skipped 169 * since this usually is caused by waiting for events via select() and co. 170 * 171 * Negative latencies (caused by time going backwards) are also explicitly 172 * skipped. 173 */ 174 void __sched 175 __account_scheduler_latency(struct task_struct *tsk, int usecs, int inter) 176 { 177 unsigned long flags; 178 int i, q; 179 struct latency_record lat; 180 181 /* Long interruptible waits are generally user requested... */ 182 if (inter && usecs > 5000) 183 return; 184 185 /* Negative sleeps are time going backwards */ 186 /* Zero-time sleeps are non-interesting */ 187 if (usecs <= 0) 188 return; 189 190 memset(&lat, 0, sizeof(lat)); 191 lat.count = 1; 192 lat.time = usecs; 193 lat.max = usecs; 194 store_stacktrace(tsk, &lat); 195 196 raw_spin_lock_irqsave(&latency_lock, flags); 197 198 account_global_scheduler_latency(tsk, &lat); 199 200 for (i = 0; i < tsk->latency_record_count; i++) { 201 struct latency_record *mylat; 202 int same = 1; 203 204 mylat = &tsk->latency_record[i]; 205 for (q = 0; q < LT_BACKTRACEDEPTH; q++) { 206 unsigned long record = lat.backtrace[q]; 207 208 if (mylat->backtrace[q] != record) { 209 same = 0; 210 break; 211 } 212 213 /* 0 and ULONG_MAX entries mean end of backtrace: */ 214 if (record == 0 || record == ULONG_MAX) 215 break; 216 } 217 if (same) { 218 mylat->count++; 219 mylat->time += lat.time; 220 if (lat.time > mylat->max) 221 mylat->max = lat.time; 222 goto out_unlock; 223 } 224 } 225 226 /* 227 * short term hack; if we're > 32 we stop; future we recycle: 228 */ 229 if (tsk->latency_record_count >= LT_SAVECOUNT) 230 goto out_unlock; 231 232 /* Allocated a new one: */ 233 i = tsk->latency_record_count++; 234 memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record)); 235 236 out_unlock: 237 raw_spin_unlock_irqrestore(&latency_lock, flags); 238 } 239 240 static int lstats_show(struct seq_file *m, void *v) 241 { 242 int i; 243 244 seq_puts(m, "Latency Top version : v0.1\n"); 245 246 for (i = 0; i < MAXLR; i++) { 247 struct latency_record *lr = &latency_record[i]; 248 249 if (lr->backtrace[0]) { 250 int q; 251 seq_printf(m, "%i %lu %lu", 252 lr->count, lr->time, lr->max); 253 for (q = 0; q < LT_BACKTRACEDEPTH; q++) { 254 unsigned long bt = lr->backtrace[q]; 255 if (!bt) 256 break; 257 if (bt == ULONG_MAX) 258 break; 259 seq_printf(m, " %ps", (void *)bt); 260 } 261 seq_puts(m, "\n"); 262 } 263 } 264 return 0; 265 } 266 267 static ssize_t 268 lstats_write(struct file *file, const char __user *buf, size_t count, 269 loff_t *offs) 270 { 271 clear_global_latency_tracing(); 272 273 return count; 274 } 275 276 static int lstats_open(struct inode *inode, struct file *filp) 277 { 278 return single_open(filp, lstats_show, NULL); 279 } 280 281 static const struct file_operations lstats_fops = { 282 .open = lstats_open, 283 .read = seq_read, 284 .write = lstats_write, 285 .llseek = seq_lseek, 286 .release = single_release, 287 }; 288 289 static int __init init_lstats_procfs(void) 290 { 291 proc_create("latency_stats", 0644, NULL, &lstats_fops); 292 return 0; 293 } 294 295 int sysctl_latencytop(struct ctl_table *table, int write, 296 void __user *buffer, size_t *lenp, loff_t *ppos) 297 { 298 int err; 299 300 err = proc_dointvec(table, write, buffer, lenp, ppos); 301 if (latencytop_enabled) 302 force_schedstat_enabled(); 303 304 return err; 305 } 306 device_initcall(init_lstats_procfs); 307