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delayacct: Account blkio completion on the correct task

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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.

With e33a9bba85, 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>
This commit is contained in:
Josh Snyder
2017-12-18 16:15:10 +00:00
committed by Ingo Molnar
parent a8750ddca9
commit c96f5471ce
3 changed files with 33 additions and 23 deletions
Download Patch File Download Diff File Expand all files Collapse all files

42
kernel/delayacct.c
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@@ -51,16 +51,16 @@ void __delayacct_tsk_init(struct task_struct *tsk)
* Finish delay accounting for a statistic using its timestamps (@start),
* accumalator (@total) and @count
*/
static void delayacct_end(u64 *start, u64 *total, u32 *count)
static void delayacct_end(spinlock_t *lock, u64 *start, u64 *total, u32 *count)
{
s64 ns = ktime_get_ns() - *start;
unsigned long flags;
if (ns > 0) {
spin_lock_irqsave(&current->delays->lock, flags);
spin_lock_irqsave(lock, flags);
*total += ns;
(*count)++;
spin_unlock_irqrestore(&current->delays->lock, flags);
spin_unlock_irqrestore(lock, flags);
}
}
@@ -69,17 +69,25 @@ void __delayacct_blkio_start(void)
current->delays->blkio_start = ktime_get_ns();
}
void __delayacct_blkio_end(void)
/*
* We cannot rely on the `current` macro, as we haven't yet switched back to
* the process being woken.
*/
void __delayacct_blkio_end(struct task_struct *p)
{
if (current->delays->flags & DELAYACCT_PF_SWAPIN)
/* Swapin block I/O */
delayacct_end(&current->delays->blkio_start,
&current->delays->swapin_delay,
&current->delays->swapin_count);
else /* Other block I/O */
delayacct_end(&current->delays->blkio_start,
&current->delays->blkio_delay,
&current->delays->blkio_count);
struct task_delay_info *delays = p->delays;
u64 *total;
u32 *count;
if (p->delays->flags & DELAYACCT_PF_SWAPIN) {
total = &delays->swapin_delay;
count = &delays->swapin_count;
} else {
total = &delays->blkio_delay;
count = &delays->blkio_count;
}
delayacct_end(&delays->lock, &delays->blkio_start, total, count);
}
int __delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk)
@@ -153,8 +161,10 @@ void __delayacct_freepages_start(void)
void __delayacct_freepages_end(void)
{
delayacct_end(&current->delays->freepages_start,
&current->delays->freepages_delay,
&current->delays->freepages_count);
delayacct_end(
&current->delays->lock,
&current->delays->freepages_start,
&current->delays->freepages_delay,
&current->delays->freepages_count);
}