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![Josh Snyder](/assets/img/avatar_default.png)
Before commit:e33a9bba85
("sched/core: move IO scheduling accounting from io_schedule_timeout() into scheduler") delayacct_blkio_end() was called after context-switching into the task which completed I/O. This resulted in double counting: the task would account a delay both waiting for I/O and for time spent in the runqueue. Withe33a9bba85
, delayacct_blkio_end() is called by try_to_wake_up(). In ttwu, we have not yet context-switched. This is more correct, in that the delay accounting ends when the I/O is complete. But delayacct_blkio_end() relies on 'get_current()', and we have not yet context-switched into the task whose I/O completed. This results in the wrong task having its delay accounting statistics updated. Instead of doing that, pass the task_struct being woken to delayacct_blkio_end(), so that it can update the statistics of the correct task. Signed-off-by: Josh Snyder <joshs@netflix.com> Acked-by: Tejun Heo <tj@kernel.org> Acked-by: Balbir Singh <bsingharora@gmail.com> Cc: <stable@vger.kernel.org> Cc: Brendan Gregg <bgregg@netflix.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-block@vger.kernel.org Fixes:e33a9bba85
("sched/core: move IO scheduling accounting from io_schedule_timeout() into scheduler") Link: http://lkml.kernel.org/r/1513613712-571-1-git-send-email-joshs@netflix.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
170 lines
4.6 KiB
C
170 lines
4.6 KiB
C
/* delayacct.c - per-task delay accounting
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*
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* Copyright (C) Shailabh Nagar, IBM Corp. 2006
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it would be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
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* the GNU General Public License for more details.
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*/
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#include <linux/sched.h>
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#include <linux/sched/task.h>
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#include <linux/sched/cputime.h>
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#include <linux/slab.h>
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#include <linux/taskstats.h>
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#include <linux/time.h>
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#include <linux/sysctl.h>
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#include <linux/delayacct.h>
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#include <linux/module.h>
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int delayacct_on __read_mostly = 1; /* Delay accounting turned on/off */
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EXPORT_SYMBOL_GPL(delayacct_on);
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struct kmem_cache *delayacct_cache;
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static int __init delayacct_setup_disable(char *str)
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{
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delayacct_on = 0;
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return 1;
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}
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__setup("nodelayacct", delayacct_setup_disable);
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void delayacct_init(void)
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{
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delayacct_cache = KMEM_CACHE(task_delay_info, SLAB_PANIC|SLAB_ACCOUNT);
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delayacct_tsk_init(&init_task);
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}
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void __delayacct_tsk_init(struct task_struct *tsk)
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{
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tsk->delays = kmem_cache_zalloc(delayacct_cache, GFP_KERNEL);
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if (tsk->delays)
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spin_lock_init(&tsk->delays->lock);
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}
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/*
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* Finish delay accounting for a statistic using its timestamps (@start),
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* accumalator (@total) and @count
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*/
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static void delayacct_end(spinlock_t *lock, u64 *start, u64 *total, u32 *count)
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{
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s64 ns = ktime_get_ns() - *start;
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unsigned long flags;
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if (ns > 0) {
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spin_lock_irqsave(lock, flags);
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*total += ns;
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(*count)++;
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spin_unlock_irqrestore(lock, flags);
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}
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}
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void __delayacct_blkio_start(void)
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{
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current->delays->blkio_start = ktime_get_ns();
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}
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/*
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* We cannot rely on the `current` macro, as we haven't yet switched back to
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* the process being woken.
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*/
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void __delayacct_blkio_end(struct task_struct *p)
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{
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struct task_delay_info *delays = p->delays;
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u64 *total;
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u32 *count;
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if (p->delays->flags & DELAYACCT_PF_SWAPIN) {
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total = &delays->swapin_delay;
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count = &delays->swapin_count;
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} else {
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total = &delays->blkio_delay;
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count = &delays->blkio_count;
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}
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delayacct_end(&delays->lock, &delays->blkio_start, total, count);
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}
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int __delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk)
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{
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u64 utime, stime, stimescaled, utimescaled;
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unsigned long long t2, t3;
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unsigned long flags, t1;
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s64 tmp;
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task_cputime(tsk, &utime, &stime);
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tmp = (s64)d->cpu_run_real_total;
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tmp += utime + stime;
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d->cpu_run_real_total = (tmp < (s64)d->cpu_run_real_total) ? 0 : tmp;
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task_cputime_scaled(tsk, &utimescaled, &stimescaled);
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tmp = (s64)d->cpu_scaled_run_real_total;
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tmp += utimescaled + stimescaled;
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d->cpu_scaled_run_real_total =
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(tmp < (s64)d->cpu_scaled_run_real_total) ? 0 : tmp;
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/*
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* No locking available for sched_info (and too expensive to add one)
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* Mitigate by taking snapshot of values
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*/
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t1 = tsk->sched_info.pcount;
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t2 = tsk->sched_info.run_delay;
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t3 = tsk->se.sum_exec_runtime;
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d->cpu_count += t1;
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tmp = (s64)d->cpu_delay_total + t2;
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d->cpu_delay_total = (tmp < (s64)d->cpu_delay_total) ? 0 : tmp;
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tmp = (s64)d->cpu_run_virtual_total + t3;
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d->cpu_run_virtual_total =
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(tmp < (s64)d->cpu_run_virtual_total) ? 0 : tmp;
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/* zero XXX_total, non-zero XXX_count implies XXX stat overflowed */
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spin_lock_irqsave(&tsk->delays->lock, flags);
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tmp = d->blkio_delay_total + tsk->delays->blkio_delay;
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d->blkio_delay_total = (tmp < d->blkio_delay_total) ? 0 : tmp;
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tmp = d->swapin_delay_total + tsk->delays->swapin_delay;
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d->swapin_delay_total = (tmp < d->swapin_delay_total) ? 0 : tmp;
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tmp = d->freepages_delay_total + tsk->delays->freepages_delay;
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d->freepages_delay_total = (tmp < d->freepages_delay_total) ? 0 : tmp;
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d->blkio_count += tsk->delays->blkio_count;
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d->swapin_count += tsk->delays->swapin_count;
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d->freepages_count += tsk->delays->freepages_count;
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spin_unlock_irqrestore(&tsk->delays->lock, flags);
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return 0;
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}
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__u64 __delayacct_blkio_ticks(struct task_struct *tsk)
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{
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__u64 ret;
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unsigned long flags;
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spin_lock_irqsave(&tsk->delays->lock, flags);
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ret = nsec_to_clock_t(tsk->delays->blkio_delay +
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tsk->delays->swapin_delay);
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spin_unlock_irqrestore(&tsk->delays->lock, flags);
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return ret;
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}
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void __delayacct_freepages_start(void)
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{
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current->delays->freepages_start = ktime_get_ns();
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}
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void __delayacct_freepages_end(void)
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{
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delayacct_end(
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¤t->delays->lock,
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¤t->delays->freepages_start,
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¤t->delays->freepages_delay,
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¤t->delays->freepages_count);
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}
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