From 57f0f512b273f60d52568b8c6b77e17f5636edc0 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Andr=C3=A9=20Fabian=20Silva=20Delgado?= Date: Wed, 5 Aug 2015 17:04:01 -0300 Subject: Initial import --- kernel/latencytop.c | 292 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 292 insertions(+) create mode 100644 kernel/latencytop.c (limited to 'kernel/latencytop.c') diff --git a/kernel/latencytop.c b/kernel/latencytop.c new file mode 100644 index 000000000..a02812743 --- /dev/null +++ b/kernel/latencytop.c @@ -0,0 +1,292 @@ +/* + * latencytop.c: Latency display infrastructure + * + * (C) Copyright 2008 Intel Corporation + * Author: Arjan van de Ven + * + * 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//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 +#include +#include +#include +#include +#include +#include +#include +#include +#include + +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; +} +device_initcall(init_lstats_procfs); -- cgit v1.2.3