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sched, latencytop: incorporate review feedback from Andrew Morton
Andrew had some suggestions for the latencytop file; this patch takes care of most of these: * Add documentation * Turn account_scheduler_latency into an inline function * Don't report negative values to userspace * Make the file operations struct const * Fix a few checkpatch.pl warnings Signed-off-by: Arjan van de Ven <arjan@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Arjan van de Ven
Ingo Molnar
parent
f437e8b53e
commit
ad0b0fd554
2 changed files with 80 additions and 13 deletions
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@ -9,6 +9,7 @@
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#ifndef _INCLUDE_GUARD_LATENCYTOP_H_
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#define _INCLUDE_GUARD_LATENCYTOP_H_
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#include <linux/compiler.h>
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#ifdef CONFIG_LATENCYTOP
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#define LT_SAVECOUNT 32
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@ -24,7 +25,14 @@ struct latency_record {
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struct task_struct;
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void account_scheduler_latency(struct task_struct *task, int usecs, int inter);
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extern int latencytop_enabled;
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void __account_scheduler_latency(struct task_struct *task, int usecs, int inter);
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static inline void
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account_scheduler_latency(struct task_struct *task, int usecs, int inter)
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{
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if (unlikely(latencytop_enabled))
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__account_scheduler_latency(task, usecs, inter);
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}
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void clear_all_latency_tracing(struct task_struct *p);
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@ -9,6 +9,44 @@
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* as published by the Free Software Foundation; version 2
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* of the License.
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*/
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/*
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* CONFIG_LATENCYTOP enables a kernel latency tracking infrastructure that is
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* used by the "latencytop" userspace tool. The latency that is tracked is not
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* the 'traditional' interrupt latency (which is primarily caused by something
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* else consuming CPU), but instead, it is the latency an application encounters
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* because the kernel sleeps on its behalf for various reasons.
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*
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* This code tracks 2 levels of statistics:
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* 1) System level latency
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* 2) Per process latency
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*
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* The latency is stored in fixed sized data structures in an accumulated form;
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* if the "same" latency cause is hit twice, this will be tracked as one entry
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* in the data structure. Both the count, total accumulated latency and maximum
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* latency are tracked in this data structure. When the fixed size structure is
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* full, no new causes are tracked until the buffer is flushed by writing to
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* the /proc file; the userspace tool does this on a regular basis.
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*
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* A latency cause is identified by a stringified backtrace at the point that
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* the scheduler gets invoked. The userland tool will use this string to
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* identify the cause of the latency in human readable form.
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*
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* The information is exported via /proc/latency_stats and /proc/<pid>/latency.
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* These files look like this:
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*
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* Latency Top version : v0.1
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* 70 59433 4897 i915_irq_wait drm_ioctl vfs_ioctl do_vfs_ioctl sys_ioctl
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* | | | |
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* | | | +----> the stringified backtrace
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* | | +---------> The maximum latency for this entry in microseconds
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* | +--------------> The accumulated latency for this entry (microseconds)
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* +-------------------> The number of times this entry is hit
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*
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* (note: the average latency is the accumulated latency divided by the number
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* of times)
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*/
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#include <linux/latencytop.h>
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#include <linux/kallsyms.h>
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#include <linux/seq_file.h>
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@ -72,7 +110,7 @@ account_global_scheduler_latency(struct task_struct *tsk, struct latency_record
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firstnonnull = i;
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continue;
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}
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for (q = 0 ; q < LT_BACKTRACEDEPTH ; q++) {
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for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
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unsigned long record = lat->backtrace[q];
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if (latency_record[i].backtrace[q] != record) {
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@ -101,31 +139,52 @@ account_global_scheduler_latency(struct task_struct *tsk, struct latency_record
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memcpy(&latency_record[i], lat, sizeof(struct latency_record));
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}
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static inline void store_stacktrace(struct task_struct *tsk, struct latency_record *lat)
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/*
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* Iterator to store a backtrace into a latency record entry
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*/
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static inline void store_stacktrace(struct task_struct *tsk,
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struct latency_record *lat)
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{
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struct stack_trace trace;
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memset(&trace, 0, sizeof(trace));
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trace.max_entries = LT_BACKTRACEDEPTH;
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trace.entries = &lat->backtrace[0];
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trace.skip = 0;
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save_stack_trace_tsk(tsk, &trace);
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}
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/**
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* __account_scheduler_latency - record an occured latency
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* @tsk - the task struct of the task hitting the latency
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* @usecs - the duration of the latency in microseconds
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* @inter - 1 if the sleep was interruptible, 0 if uninterruptible
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*
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* This function is the main entry point for recording latency entries
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* as called by the scheduler.
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*
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* This function has a few special cases to deal with normal 'non-latency'
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* sleeps: specifically, interruptible sleep longer than 5 msec is skipped
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* since this usually is caused by waiting for events via select() and co.
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*
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* Negative latencies (caused by time going backwards) are also explicitly
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* skipped.
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*/
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void __sched
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account_scheduler_latency(struct task_struct *tsk, int usecs, int inter)
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__account_scheduler_latency(struct task_struct *tsk, int usecs, int inter)
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{
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unsigned long flags;
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int i, q;
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struct latency_record lat;
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if (!latencytop_enabled)
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return;
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/* Long interruptible waits are generally user requested... */
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if (inter && usecs > 5000)
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return;
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/* Negative sleeps are time going backwards */
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/* Zero-time sleeps are non-interesting */
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if (usecs <= 0)
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return;
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memset(&lat, 0, sizeof(lat));
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lat.count = 1;
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lat.time = usecs;
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@ -143,12 +202,12 @@ account_scheduler_latency(struct task_struct *tsk, int usecs, int inter)
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if (tsk->latency_record_count >= LT_SAVECOUNT)
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goto out_unlock;
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for (i = 0; i < LT_SAVECOUNT ; i++) {
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for (i = 0; i < LT_SAVECOUNT; i++) {
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struct latency_record *mylat;
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int same = 1;
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mylat = &tsk->latency_record[i];
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for (q = 0 ; q < LT_BACKTRACEDEPTH ; q++) {
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for (q = 0; q < LT_BACKTRACEDEPTH; q++) {
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unsigned long record = lat.backtrace[q];
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if (mylat->backtrace[q] != record) {
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@ -186,7 +245,7 @@ static int lstats_show(struct seq_file *m, void *v)
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for (i = 0; i < MAXLR; i++) {
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if (latency_record[i].backtrace[0]) {
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int q;
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seq_printf(m, "%i %li %li ",
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seq_printf(m, "%i %lu %lu ",
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latency_record[i].count,
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latency_record[i].time,
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latency_record[i].max);
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@ -223,7 +282,7 @@ static int lstats_open(struct inode *inode, struct file *filp)
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return single_open(filp, lstats_show, NULL);
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}
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static struct file_operations lstats_fops = {
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static const struct file_operations lstats_fops = {
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.open = lstats_open,
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.read = seq_read,
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.write = lstats_write,
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@ -236,4 +295,4 @@ static int __init init_lstats_procfs(void)
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proc_create("latency_stats", 0644, NULL, &lstats_fops);
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return 0;
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}
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__initcall(init_lstats_procfs);
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device_initcall(init_lstats_procfs);
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