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 entry marks end of backtrace: */ 124 if (!record) 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 * __account_scheduler_latency - record an occurred latency 146 * @tsk - the task struct of the task hitting the latency 147 * @usecs - the duration of the latency in microseconds 148 * @inter - 1 if the sleep was interruptible, 0 if uninterruptible 149 * 150 * This function is the main entry point for recording latency entries 151 * as called by the scheduler. 152 * 153 * This function has a few special cases to deal with normal 'non-latency' 154 * sleeps: specifically, interruptible sleep longer than 5 msec is skipped 155 * since this usually is caused by waiting for events via select() and co. 156 * 157 * Negative latencies (caused by time going backwards) are also explicitly 158 * skipped. 159 */ 160 void __sched 161 __account_scheduler_latency(struct task_struct *tsk, int usecs, int inter) 162 { 163 unsigned long flags; 164 int i, q; 165 struct latency_record lat; 166 167 /* Long interruptible waits are generally user requested... */ 168 if (inter && usecs > 5000) 169 return; 170 171 /* Negative sleeps are time going backwards */ 172 /* Zero-time sleeps are non-interesting */ 173 if (usecs <= 0) 174 return; 175 176 memset(&lat, 0, sizeof(lat)); 177 lat.count = 1; 178 lat.time = usecs; 179 lat.max = usecs; 180 181 stack_trace_save_tsk(tsk, lat.backtrace, LT_BACKTRACEDEPTH, 0); 182 183 raw_spin_lock_irqsave(&latency_lock, flags); 184 185 account_global_scheduler_latency(tsk, &lat); 186 187 for (i = 0; i < tsk->latency_record_count; i++) { 188 struct latency_record *mylat; 189 int same = 1; 190 191 mylat = &tsk->latency_record[i]; 192 for (q = 0; q < LT_BACKTRACEDEPTH; q++) { 193 unsigned long record = lat.backtrace[q]; 194 195 if (mylat->backtrace[q] != record) { 196 same = 0; 197 break; 198 } 199 200 /* 0 entry is end of backtrace */ 201 if (!record) 202 break; 203 } 204 if (same) { 205 mylat->count++; 206 mylat->time += lat.time; 207 if (lat.time > mylat->max) 208 mylat->max = lat.time; 209 goto out_unlock; 210 } 211 } 212 213 /* 214 * short term hack; if we're > 32 we stop; future we recycle: 215 */ 216 if (tsk->latency_record_count >= LT_SAVECOUNT) 217 goto out_unlock; 218 219 /* Allocated a new one: */ 220 i = tsk->latency_record_count++; 221 memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record)); 222 223 out_unlock: 224 raw_spin_unlock_irqrestore(&latency_lock, flags); 225 } 226 227 static int lstats_show(struct seq_file *m, void *v) 228 { 229 int i; 230 231 seq_puts(m, "Latency Top version : v0.1\n"); 232 233 for (i = 0; i < MAXLR; i++) { 234 struct latency_record *lr = &latency_record[i]; 235 236 if (lr->backtrace[0]) { 237 int q; 238 seq_printf(m, "%i %lu %lu", 239 lr->count, lr->time, lr->max); 240 for (q = 0; q < LT_BACKTRACEDEPTH; q++) { 241 unsigned long bt = lr->backtrace[q]; 242 243 if (!bt) 244 break; 245 246 seq_printf(m, " %ps", (void *)bt); 247 } 248 seq_puts(m, "\n"); 249 } 250 } 251 return 0; 252 } 253 254 static ssize_t 255 lstats_write(struct file *file, const char __user *buf, size_t count, 256 loff_t *offs) 257 { 258 clear_global_latency_tracing(); 259 260 return count; 261 } 262 263 static int lstats_open(struct inode *inode, struct file *filp) 264 { 265 return single_open(filp, lstats_show, NULL); 266 } 267 268 static const struct file_operations lstats_fops = { 269 .open = lstats_open, 270 .read = seq_read, 271 .write = lstats_write, 272 .llseek = seq_lseek, 273 .release = single_release, 274 }; 275 276 static int __init init_lstats_procfs(void) 277 { 278 proc_create("latency_stats", 0644, NULL, &lstats_fops); 279 return 0; 280 } 281 282 int sysctl_latencytop(struct ctl_table *table, int write, 283 void __user *buffer, size_t *lenp, loff_t *ppos) 284 { 285 int err; 286 287 err = proc_dointvec(table, write, buffer, lenp, ppos); 288 if (latencytop_enabled) 289 force_schedstat_enabled(); 290 291 return err; 292 } 293 device_initcall(init_lstats_procfs); 294