Commit-ID: c96f5471ce7d2aefd0dda560cc23f08ab00bc65d Gitweb: https://git.kernel.org/tip/c96f5471ce7d2aefd0dda560cc23f08ab00bc65d Author: Josh Snyder joshs@netflix.com AuthorDate: Mon, 18 Dec 2017 16:15:10 +0000 Committer: Ingo Molnar mingo@kernel.org CommitDate: Tue, 16 Jan 2018 03:29:36 +0100

delayacct: Account blkio completion on the correct task

Before commit:

e33a9bba85a8 ("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 e33a9bba85a8, 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: e33a9bba85a8 ("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 --- include/linux/delayacct.h | 8 ++++---- kernel/delayacct.c | 42 ++++++++++++++++++++++++++---------------- kernel/sched/core.c | 6 +++--- 3 files changed, 33 insertions(+), 23 deletions(-)

diff --git a/include/linux/delayacct.h b/include/linux/delayacct.h index 4178d24..5e335b6 100644 --- a/include/linux/delayacct.h +++ b/include/linux/delayacct.h @@ -71,7 +71,7 @@ extern void delayacct_init(void); extern void __delayacct_tsk_init(struct task_struct *); extern void __delayacct_tsk_exit(struct task_struct *); extern void __delayacct_blkio_start(void); -extern void __delayacct_blkio_end(void); +extern void __delayacct_blkio_end(struct task_struct *); extern int __delayacct_add_tsk(struct taskstats *, struct task_struct *); extern __u64 __delayacct_blkio_ticks(struct task_struct *); extern void __delayacct_freepages_start(void); @@ -122,10 +122,10 @@ static inline void delayacct_blkio_start(void) __delayacct_blkio_start(); }

-static inline void delayacct_blkio_end(void) +static inline void delayacct_blkio_end(struct task_struct *p) { if (current->delays) - __delayacct_blkio_end(); + __delayacct_blkio_end(p); delayacct_clear_flag(DELAYACCT_PF_BLKIO); }

@@ -169,7 +169,7 @@ static inline void delayacct_tsk_free(struct task_struct *tsk) {} static inline void delayacct_blkio_start(void) {} -static inline void delayacct_blkio_end(void) +static inline void delayacct_blkio_end(struct task_struct *p) {} static inline int delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk) diff --git a/kernel/delayacct.c b/kernel/delayacct.c index 4a1c334..e2764d7 100644 --- a/kernel/delayacct.c +++ b/kernel/delayacct.c @@ -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); }

diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 644fa2e..a7bf32a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2056,7 +2056,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) p->state = TASK_WAKING;

if (p->in_iowait) { - delayacct_blkio_end(); + delayacct_blkio_end(p); atomic_dec(&task_rq(p)->nr_iowait); }

@@ -2069,7 +2069,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) #else /* CONFIG_SMP */

if (p->in_iowait) { - delayacct_blkio_end(); + delayacct_blkio_end(p); atomic_dec(&task_rq(p)->nr_iowait); }

@@ -2122,7 +2122,7 @@ static void try_to_wake_up_local(struct task_struct *p, struct rq_flags *rf)

if (!task_on_rq_queued(p)) { if (p->in_iowait) { - delayacct_blkio_end(); + delayacct_blkio_end(p); atomic_dec(&rq->nr_iowait); } ttwu_activate(rq, p, ENQUEUE_WAKEUP | ENQUEUE_NOCLOCK);