Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756361AbdLOSLu (ORCPT ); Fri, 15 Dec 2017 13:11:50 -0500 Received: from mail-pg0-f68.google.com ([74.125.83.68]:33892 "EHLO mail-pg0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756148AbdLOSLp (ORCPT ); Fri, 15 Dec 2017 13:11:45 -0500 X-Google-Smtp-Source: ACJfBotcK23ElR4GYudbeqlVIG96jMzM6xysg2OYqrEUcOGFVybq2+oLBC6m8tuBwOVhx09bAYE9XA== From: Josh Snyder To: linux-kernel@vger.kernel.org Cc: Jens Axboe , Brendan Gregg , linux-block@vger.kernel.org, Tejun Heo , Josh Snyder , Balbir Singh , Ingo Molnar , Peter Zijlstra Subject: [PATCH] Pass the task_struct explicitly to delayacct_blkio_end Date: Fri, 15 Dec 2017 18:11:43 +0000 Message-Id: <1513361505-275-1-git-send-email-joshs@netflix.com> X-Mailer: git-send-email 2.7.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5517 Lines: 163 Before e33a9bba85a8, 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 upon `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_struct. --- 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..f2ad868 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..e2ec808 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(¤t->delays->lock, flags); + spin_lock_irqsave(lock, flags); *total += ns; (*count)++; - spin_unlock_irqrestore(¤t->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(¤t->delays->blkio_start, - ¤t->delays->swapin_delay, - ¤t->delays->swapin_count); - else /* Other block I/O */ - delayacct_end(¤t->delays->blkio_start, - ¤t->delays->blkio_delay, - ¤t->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(¤t->delays->freepages_start, - ¤t->delays->freepages_delay, - ¤t->delays->freepages_count); + delayacct_end( + ¤t->delays->lock, + ¤t->delays->freepages_start, + ¤t->delays->freepages_delay, + ¤t->delays->freepages_count); } diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 75554f3..deda018 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); -- 2.7.4