1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * latencytop.c: Latency display infrastructure 4 * 5 * (C) Copyright 2008 Intel Corporation 6 * Author: Arjan van de Ven <arjan@linux.intel.com> 7 */ 8 9 /* 10 * CONFIG_LATENCYTOP enables a kernel latency tracking infrastructure that is 11 * used by the "latencytop" userspace tool. The latency that is tracked is not 12 * the 'traditional' interrupt latency (which is primarily caused by something 13 * else consuming CPU), but instead, it is the latency an application encounters 14 * because the kernel sleeps on its behalf for various reasons. 15 * 16 * This code tracks 2 levels of statistics: 17 * 1) System level latency 18 * 2) Per process latency 19 * 20 * The latency is stored in fixed sized data structures in an accumulated form; 21 * if the "same" latency cause is hit twice, this will be tracked as one entry 22 * in the data structure. Both the count, total accumulated latency and maximum 23 * latency are tracked in this data structure. When the fixed size structure is 24 * full, no new causes are tracked until the buffer is flushed by writing to 25 * the /proc file; the userspace tool does this on a regular basis. 26 * 27 * A latency cause is identified by a stringified backtrace at the point that 28 * the scheduler gets invoked. The userland tool will use this string to 29 * identify the cause of the latency in human readable form. 30 * 31 * The information is exported via /proc/latency_stats and /proc/<pid>/latency. 32 * These files look like this: 33 * 34 * Latency Top version : v0.1 35 * 70 59433 4897 i915_irq_wait drm_ioctl vfs_ioctl do_vfs_ioctl sys_ioctl 36 * | | | | 37 * | | | +----> the stringified backtrace 38 * | | +---------> The maximum latency for this entry in microseconds 39 * | +--------------> The accumulated latency for this entry (microseconds) 40 * +-------------------> The number of times this entry is hit 41 * 42 * (note: the average latency is the accumulated latency divided by the number 43 * of times) 44 */ 45 46 #include <linux/kallsyms.h> 47 #include <linux/seq_file.h> 48 #include <linux/notifier.h> 49 #include <linux/spinlock.h> 50 #include <linux/proc_fs.h> 51 #include <linux/latencytop.h> 52 #include <linux/export.h> 53 #include <linux/sched.h> 54 #include <linux/sched/debug.h> 55 #include <linux/sched/stat.h> 56 #include <linux/list.h> 57 #include <linux/stacktrace.h> 58 #include <linux/sysctl.h> 59 60 static DEFINE_RAW_SPINLOCK(latency_lock); 61 62 #define MAXLR 128 63 static struct latency_record latency_record[MAXLR]; 64 65 int latencytop_enabled; 66 67 #ifdef CONFIG_SYSCTL 68 static int sysctl_latencytop(struct ctl_table *table, int write, void *buffer, 69 size_t *lenp, loff_t *ppos) 70 { 71 int err; 72 73 err = proc_dointvec(table, write, buffer, lenp, ppos); 74 if (latencytop_enabled) 75 force_schedstat_enabled(); 76 77 return err; 78 } 79 80 static struct ctl_table latencytop_sysctl[] = { 81 { 82 .procname = "latencytop", 83 .data = &latencytop_enabled, 84 .maxlen = sizeof(int), 85 .mode = 0644, 86 .proc_handler = sysctl_latencytop, 87 }, 88 {} 89 }; 90 #endif 91 92 void clear_tsk_latency_tracing(struct task_struct *p) 93 { 94 unsigned long flags; 95 96 raw_spin_lock_irqsave(&latency_lock, flags); 97 memset(&p->latency_record, 0, sizeof(p->latency_record)); 98 p->latency_record_count = 0; 99 raw_spin_unlock_irqrestore(&latency_lock, flags); 100 } 101 102 static void clear_global_latency_tracing(void) 103 { 104 unsigned long flags; 105 106 raw_spin_lock_irqsave(&latency_lock, flags); 107 memset(&latency_record, 0, sizeof(latency_record)); 108 raw_spin_unlock_irqrestore(&latency_lock, flags); 109 } 110 111 static void __sched 112 account_global_scheduler_latency(struct task_struct *tsk, 113 struct latency_record *lat) 114 { 115 int firstnonnull = MAXLR + 1; 116 int i; 117 118 /* skip kernel threads for now */ 119 if (!tsk->mm) 120 return; 121 122 for (i = 0; i < MAXLR; i++) { 123 int q, same = 1; 124 125 /* Nothing stored: */ 126 if (!latency_record[i].backtrace[0]) { 127 if (firstnonnull > i) 128 firstnonnull = i; 129 continue; 130 } 131 for (q = 0; q < LT_BACKTRACEDEPTH; q++) { 132 unsigned long record = lat->backtrace[q]; 133 134 if (latency_record[i].backtrace[q] != record) { 135 same = 0; 136 break; 137 } 138 139 /* 0 entry marks end of backtrace: */ 140 if (!record) 141 break; 142 } 143 if (same) { 144 latency_record[i].count++; 145 latency_record[i].time += lat->time; 146 if (lat->time > latency_record[i].max) 147 latency_record[i].max = lat->time; 148 return; 149 } 150 } 151 152 i = firstnonnull; 153 if (i >= MAXLR - 1) 154 return; 155 156 /* Allocted a new one: */ 157 memcpy(&latency_record[i], lat, sizeof(struct latency_record)); 158 } 159 160 /** 161 * __account_scheduler_latency - record an occurred latency 162 * @tsk - the task struct of the task hitting the latency 163 * @usecs - the duration of the latency in microseconds 164 * @inter - 1 if the sleep was interruptible, 0 if uninterruptible 165 * 166 * This function is the main entry point for recording latency entries 167 * as called by the scheduler. 168 * 169 * This function has a few special cases to deal with normal 'non-latency' 170 * sleeps: specifically, interruptible sleep longer than 5 msec is skipped 171 * since this usually is caused by waiting for events via select() and co. 172 * 173 * Negative latencies (caused by time going backwards) are also explicitly 174 * skipped. 175 */ 176 void __sched 177 __account_scheduler_latency(struct task_struct *tsk, int usecs, int inter) 178 { 179 unsigned long flags; 180 int i, q; 181 struct latency_record lat; 182 183 /* Long interruptible waits are generally user requested... */ 184 if (inter && usecs > 5000) 185 return; 186 187 /* Negative sleeps are time going backwards */ 188 /* Zero-time sleeps are non-interesting */ 189 if (usecs <= 0) 190 return; 191 192 memset(&lat, 0, sizeof(lat)); 193 lat.count = 1; 194 lat.time = usecs; 195 lat.max = usecs; 196 197 stack_trace_save_tsk(tsk, lat.backtrace, LT_BACKTRACEDEPTH, 0); 198 199 raw_spin_lock_irqsave(&latency_lock, flags); 200 201 account_global_scheduler_latency(tsk, &lat); 202 203 for (i = 0; i < tsk->latency_record_count; i++) { 204 struct latency_record *mylat; 205 int same = 1; 206 207 mylat = &tsk->latency_record[i]; 208 for (q = 0; q < LT_BACKTRACEDEPTH; q++) { 209 unsigned long record = lat.backtrace[q]; 210 211 if (mylat->backtrace[q] != record) { 212 same = 0; 213 break; 214 } 215 216 /* 0 entry is end of backtrace */ 217 if (!record) 218 break; 219 } 220 if (same) { 221 mylat->count++; 222 mylat->time += lat.time; 223 if (lat.time > mylat->max) 224 mylat->max = lat.time; 225 goto out_unlock; 226 } 227 } 228 229 /* 230 * short term hack; if we're > 32 we stop; future we recycle: 231 */ 232 if (tsk->latency_record_count >= LT_SAVECOUNT) 233 goto out_unlock; 234 235 /* Allocated a new one: */ 236 i = tsk->latency_record_count++; 237 memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record)); 238 239 out_unlock: 240 raw_spin_unlock_irqrestore(&latency_lock, flags); 241 } 242 243 static int lstats_show(struct seq_file *m, void *v) 244 { 245 int i; 246 247 seq_puts(m, "Latency Top version : v0.1\n"); 248 249 for (i = 0; i < MAXLR; i++) { 250 struct latency_record *lr = &latency_record[i]; 251 252 if (lr->backtrace[0]) { 253 int q; 254 seq_printf(m, "%i %lu %lu", 255 lr->count, lr->time, lr->max); 256 for (q = 0; q < LT_BACKTRACEDEPTH; q++) { 257 unsigned long bt = lr->backtrace[q]; 258 259 if (!bt) 260 break; 261 262 seq_printf(m, " %ps", (void *)bt); 263 } 264 seq_puts(m, "\n"); 265 } 266 } 267 return 0; 268 } 269 270 static ssize_t 271 lstats_write(struct file *file, const char __user *buf, size_t count, 272 loff_t *offs) 273 { 274 clear_global_latency_tracing(); 275 276 return count; 277 } 278 279 static int lstats_open(struct inode *inode, struct file *filp) 280 { 281 return single_open(filp, lstats_show, NULL); 282 } 283 284 static const struct proc_ops lstats_proc_ops = { 285 .proc_open = lstats_open, 286 .proc_read = seq_read, 287 .proc_write = lstats_write, 288 .proc_lseek = seq_lseek, 289 .proc_release = single_release, 290 }; 291 292 static int __init init_lstats_procfs(void) 293 { 294 proc_create("latency_stats", 0644, NULL, &lstats_proc_ops); 295 #ifdef CONFIG_SYSCTL 296 register_sysctl_init("kernel", latencytop_sysctl); 297 #endif 298 return 0; 299 } 300 device_initcall(init_lstats_procfs); 301