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/latencytop.h> 51 #include <linux/kallsyms.h> 52 #include <linux/seq_file.h> 53 #include <linux/notifier.h> 54 #include <linux/spinlock.h> 55 #include <linux/proc_fs.h> 56 #include <linux/module.h> 57 #include <linux/sched.h> 58 #include <linux/list.h> 59 #include <linux/slab.h> 60 #include <linux/stacktrace.h> 61 62 static DEFINE_SPINLOCK(latency_lock); 63 64 #define MAXLR 128 65 static struct latency_record latency_record[MAXLR]; 66 67 int latencytop_enabled; 68 69 void clear_all_latency_tracing(struct task_struct *p) 70 { 71 unsigned long flags; 72 73 if (!latencytop_enabled) 74 return; 75 76 spin_lock_irqsave(&latency_lock, flags); 77 memset(&p->latency_record, 0, sizeof(p->latency_record)); 78 p->latency_record_count = 0; 79 spin_unlock_irqrestore(&latency_lock, flags); 80 } 81 82 static void clear_global_latency_tracing(void) 83 { 84 unsigned long flags; 85 86 spin_lock_irqsave(&latency_lock, flags); 87 memset(&latency_record, 0, sizeof(latency_record)); 88 spin_unlock_irqrestore(&latency_lock, flags); 89 } 90 91 static void __sched 92 account_global_scheduler_latency(struct task_struct *tsk, 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 occured 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 spin_lock_irqsave(&latency_lock, flags); 195 196 account_global_scheduler_latency(tsk, &lat); 197 198 /* 199 * short term hack; if we're > 32 we stop; future we recycle: 200 */ 201 tsk->latency_record_count++; 202 if (tsk->latency_record_count >= LT_SAVECOUNT) 203 goto out_unlock; 204 205 for (i = 0; i < LT_SAVECOUNT; i++) { 206 struct latency_record *mylat; 207 int same = 1; 208 209 mylat = &tsk->latency_record[i]; 210 for (q = 0; q < LT_BACKTRACEDEPTH; q++) { 211 unsigned long record = lat.backtrace[q]; 212 213 if (mylat->backtrace[q] != record) { 214 same = 0; 215 break; 216 } 217 218 /* 0 and ULONG_MAX entries mean end of backtrace: */ 219 if (record == 0 || record == ULONG_MAX) 220 break; 221 } 222 if (same) { 223 mylat->count++; 224 mylat->time += lat.time; 225 if (lat.time > mylat->max) 226 mylat->max = lat.time; 227 goto out_unlock; 228 } 229 } 230 231 /* Allocated a new one: */ 232 i = tsk->latency_record_count; 233 memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record)); 234 235 out_unlock: 236 spin_unlock_irqrestore(&latency_lock, flags); 237 } 238 239 static int lstats_show(struct seq_file *m, void *v) 240 { 241 int i; 242 243 seq_puts(m, "Latency Top version : v0.1\n"); 244 245 for (i = 0; i < MAXLR; i++) { 246 if (latency_record[i].backtrace[0]) { 247 int q; 248 seq_printf(m, "%i %lu %lu ", 249 latency_record[i].count, 250 latency_record[i].time, 251 latency_record[i].max); 252 for (q = 0; q < LT_BACKTRACEDEPTH; q++) { 253 char sym[KSYM_SYMBOL_LEN]; 254 char *c; 255 if (!latency_record[i].backtrace[q]) 256 break; 257 if (latency_record[i].backtrace[q] == ULONG_MAX) 258 break; 259 sprint_symbol(sym, latency_record[i].backtrace[q]); 260 c = strchr(sym, '+'); 261 if (c) 262 *c = 0; 263 seq_printf(m, "%s ", sym); 264 } 265 seq_printf(m, "\n"); 266 } 267 } 268 return 0; 269 } 270 271 static ssize_t 272 lstats_write(struct file *file, const char __user *buf, size_t count, 273 loff_t *offs) 274 { 275 clear_global_latency_tracing(); 276 277 return count; 278 } 279 280 static int lstats_open(struct inode *inode, struct file *filp) 281 { 282 return single_open(filp, lstats_show, NULL); 283 } 284 285 static const struct file_operations lstats_fops = { 286 .open = lstats_open, 287 .read = seq_read, 288 .write = lstats_write, 289 .llseek = seq_lseek, 290 .release = single_release, 291 }; 292 293 static int __init init_lstats_procfs(void) 294 { 295 proc_create("latency_stats", 0644, NULL, &lstats_fops); 296 return 0; 297 } 298 device_initcall(init_lstats_procfs); 299