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