| /* |
| * latencytop.c: Latency display infrastructure |
| * |
| * (C) Copyright 2008 Intel Corporation |
| * Author: Arjan van de Ven <arjan@linux.intel.com> |
| * |
| * This program is free software; you can redistribute it and/or |
| * modify it under the terms of the GNU General Public License |
| * as published by the Free Software Foundation; version 2 |
| * of the License. |
| */ |
| |
| /* |
| * CONFIG_LATENCYTOP enables a kernel latency tracking infrastructure that is |
| * used by the "latencytop" userspace tool. The latency that is tracked is not |
| * the 'traditional' interrupt latency (which is primarily caused by something |
| * else consuming CPU), but instead, it is the latency an application encounters |
| * because the kernel sleeps on its behalf for various reasons. |
| * |
| * This code tracks 2 levels of statistics: |
| * 1) System level latency |
| * 2) Per process latency |
| * |
| * The latency is stored in fixed sized data structures in an accumulated form; |
| * if the "same" latency cause is hit twice, this will be tracked as one entry |
| * in the data structure. Both the count, total accumulated latency and maximum |
| * latency are tracked in this data structure. When the fixed size structure is |
| * full, no new causes are tracked until the buffer is flushed by writing to |
| * the /proc file; the userspace tool does this on a regular basis. |
| * |
| * A latency cause is identified by a stringified backtrace at the point that |
| * the scheduler gets invoked. The userland tool will use this string to |
| * identify the cause of the latency in human readable form. |
| * |
| * The information is exported via /proc/latency_stats and /proc/<pid>/latency. |
| * These files look like this: |
| * |
| * Latency Top version : v0.1 |
| * 70 59433 4897 i915_irq_wait drm_ioctl vfs_ioctl do_vfs_ioctl sys_ioctl |
| * | | | | |
| * | | | +----> the stringified backtrace |
| * | | +---------> The maximum latency for this entry in microseconds |
| * | +--------------> The accumulated latency for this entry (microseconds) |
| * +-------------------> The number of times this entry is hit |
| * |
| * (note: the average latency is the accumulated latency divided by the number |
| * of times) |
| */ |
| |
| #include <linux/kallsyms.h> |
| #include <linux/seq_file.h> |
| #include <linux/notifier.h> |
| #include <linux/spinlock.h> |
| #include <linux/proc_fs.h> |
| #include <linux/latencytop.h> |
| #include <linux/export.h> |
| #include <linux/sched.h> |
| #include <linux/sched/debug.h> |
| #include <linux/sched/stat.h> |
| #include <linux/list.h> |
| #include <linux/stacktrace.h> |
| |
| static DEFINE_RAW_SPINLOCK(latency_lock); |
| |
| #define MAXLR 128 |
| static struct latency_record latency_record[MAXLR]; |
| |
| int latencytop_enabled; |
| |
| void clear_all_latency_tracing(struct task_struct *p) |
| { |
| unsigned long flags; |
| |
| if (!latencytop_enabled) |
| return; |
| |
| raw_spin_lock_irqsave(&latency_lock, flags); |
| memset(&p->latency_record, 0, sizeof(p->latency_record)); |
| p->latency_record_count = 0; |
| raw_spin_unlock_irqrestore(&latency_lock, flags); |
| } |
| |
| static void clear_global_latency_tracing(void) |
| { |
| unsigned long flags; |
| |
| raw_spin_lock_irqsave(&latency_lock, flags); |
| memset(&latency_record, 0, sizeof(latency_record)); |
| raw_spin_unlock_irqrestore(&latency_lock, flags); |
| } |
| |
| static void __sched |
| account_global_scheduler_latency(struct task_struct *tsk, |
| struct latency_record *lat) |
| { |
| int firstnonnull = MAXLR + 1; |
| int i; |
| |
| if (!latencytop_enabled) |
| return; |
| |
| /* skip kernel threads for now */ |
| if (!tsk->mm) |
| return; |
| |
| for (i = 0; i < MAXLR; i++) { |
| int q, same = 1; |
| |
| /* Nothing stored: */ |
| if (!latency_record[i].backtrace[0]) { |
| if (firstnonnull > i) |
| firstnonnull = i; |
| continue; |
| } |
| for (q = 0; q < LT_BACKTRACEDEPTH; q++) { |
| unsigned long record = lat->backtrace[q]; |
| |
| if (latency_record[i].backtrace[q] != record) { |
| same = 0; |
| break; |
| } |
| |
| /* 0 and ULONG_MAX entries mean end of backtrace: */ |
| if (record == 0 || record == ULONG_MAX) |
| break; |
| } |
| if (same) { |
| latency_record[i].count++; |
| latency_record[i].time += lat->time; |
| if (lat->time > latency_record[i].max) |
| latency_record[i].max = lat->time; |
| return; |
| } |
| } |
| |
| i = firstnonnull; |
| if (i >= MAXLR - 1) |
| return; |
| |
| /* Allocted a new one: */ |
| memcpy(&latency_record[i], lat, sizeof(struct latency_record)); |
| } |
| |
| /* |
| * Iterator to store a backtrace into a latency record entry |
| */ |
| static inline void store_stacktrace(struct task_struct *tsk, |
| struct latency_record *lat) |
| { |
| struct stack_trace trace; |
| |
| memset(&trace, 0, sizeof(trace)); |
| trace.max_entries = LT_BACKTRACEDEPTH; |
| trace.entries = &lat->backtrace[0]; |
| save_stack_trace_tsk(tsk, &trace); |
| } |
| |
| /** |
| * __account_scheduler_latency - record an occurred latency |
| * @tsk - the task struct of the task hitting the latency |
| * @usecs - the duration of the latency in microseconds |
| * @inter - 1 if the sleep was interruptible, 0 if uninterruptible |
| * |
| * This function is the main entry point for recording latency entries |
| * as called by the scheduler. |
| * |
| * This function has a few special cases to deal with normal 'non-latency' |
| * sleeps: specifically, interruptible sleep longer than 5 msec is skipped |
| * since this usually is caused by waiting for events via select() and co. |
| * |
| * Negative latencies (caused by time going backwards) are also explicitly |
| * skipped. |
| */ |
| void __sched |
| __account_scheduler_latency(struct task_struct *tsk, int usecs, int inter) |
| { |
| unsigned long flags; |
| int i, q; |
| struct latency_record lat; |
| |
| /* Long interruptible waits are generally user requested... */ |
| if (inter && usecs > 5000) |
| return; |
| |
| /* Negative sleeps are time going backwards */ |
| /* Zero-time sleeps are non-interesting */ |
| if (usecs <= 0) |
| return; |
| |
| memset(&lat, 0, sizeof(lat)); |
| lat.count = 1; |
| lat.time = usecs; |
| lat.max = usecs; |
| store_stacktrace(tsk, &lat); |
| |
| raw_spin_lock_irqsave(&latency_lock, flags); |
| |
| account_global_scheduler_latency(tsk, &lat); |
| |
| for (i = 0; i < tsk->latency_record_count; i++) { |
| struct latency_record *mylat; |
| int same = 1; |
| |
| mylat = &tsk->latency_record[i]; |
| for (q = 0; q < LT_BACKTRACEDEPTH; q++) { |
| unsigned long record = lat.backtrace[q]; |
| |
| if (mylat->backtrace[q] != record) { |
| same = 0; |
| break; |
| } |
| |
| /* 0 and ULONG_MAX entries mean end of backtrace: */ |
| if (record == 0 || record == ULONG_MAX) |
| break; |
| } |
| if (same) { |
| mylat->count++; |
| mylat->time += lat.time; |
| if (lat.time > mylat->max) |
| mylat->max = lat.time; |
| goto out_unlock; |
| } |
| } |
| |
| /* |
| * short term hack; if we're > 32 we stop; future we recycle: |
| */ |
| if (tsk->latency_record_count >= LT_SAVECOUNT) |
| goto out_unlock; |
| |
| /* Allocated a new one: */ |
| i = tsk->latency_record_count++; |
| memcpy(&tsk->latency_record[i], &lat, sizeof(struct latency_record)); |
| |
| out_unlock: |
| raw_spin_unlock_irqrestore(&latency_lock, flags); |
| } |
| |
| static int lstats_show(struct seq_file *m, void *v) |
| { |
| int i; |
| |
| seq_puts(m, "Latency Top version : v0.1\n"); |
| |
| for (i = 0; i < MAXLR; i++) { |
| struct latency_record *lr = &latency_record[i]; |
| |
| if (lr->backtrace[0]) { |
| int q; |
| seq_printf(m, "%i %lu %lu", |
| lr->count, lr->time, lr->max); |
| for (q = 0; q < LT_BACKTRACEDEPTH; q++) { |
| unsigned long bt = lr->backtrace[q]; |
| if (!bt) |
| break; |
| if (bt == ULONG_MAX) |
| break; |
| seq_printf(m, " %ps", (void *)bt); |
| } |
| seq_puts(m, "\n"); |
| } |
| } |
| return 0; |
| } |
| |
| static ssize_t |
| lstats_write(struct file *file, const char __user *buf, size_t count, |
| loff_t *offs) |
| { |
| clear_global_latency_tracing(); |
| |
| return count; |
| } |
| |
| static int lstats_open(struct inode *inode, struct file *filp) |
| { |
| return single_open(filp, lstats_show, NULL); |
| } |
| |
| static const struct file_operations lstats_fops = { |
| .open = lstats_open, |
| .read = seq_read, |
| .write = lstats_write, |
| .llseek = seq_lseek, |
| .release = single_release, |
| }; |
| |
| static int __init init_lstats_procfs(void) |
| { |
| proc_create("latency_stats", 0644, NULL, &lstats_fops); |
| return 0; |
| } |
| |
| int sysctl_latencytop(struct ctl_table *table, int write, |
| void __user *buffer, size_t *lenp, loff_t *ppos) |
| { |
| int err; |
| |
| err = proc_dointvec(table, write, buffer, lenp, ppos); |
| if (latencytop_enabled) |
| force_schedstat_enabled(); |
| |
| return err; |
| } |
| device_initcall(init_lstats_procfs); |