| 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); |