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Patch "delayacct: Account blkio completion on the correct task" has been added to the 4.14-stable tree

PATCH [email protected] 1 participant 1 message Jan 18, 2018

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Stable branch Scheduler Per-task delay accounting
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This is a note to let you know that I've just added the patch titled

delayacct: Account blkio completion on the correct task

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
delayacct-account-blkio-completion-on-the-correct-task.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From c96f5471ce7d2aefd0dda560cc23f08ab00bc65d Mon Sep 17 00:00:00 2001

From: Josh Snyder <[email protected]>
Date: Mon, 18 Dec 2017 16:15:10 +0000
Subject: delayacct: Account blkio completion on the correct task

From: Josh Snyder <[email protected]>

commit c96f5471ce7d2aefd0dda560cc23f08ab00bc65d upstream.

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 <[email protected]>
Acked-by Tejun Heo <[email protected]>
Acked-by Balbir Singh <[email protected]>
Cc Brendan Gregg <[email protected]>
Cc Jens Axboe <[email protected]>
Cc Linus Torvalds <[email protected]>
Cc Peter Zijlstra <[email protected]>
Cc Thomas Gleixner <[email protected]>
Cc [email protected]
Fixes e33a9bba85a8 ("sched/core: move IO scheduling accounting from io_schedule_timeout() into scheduler")
Link http://lkml.kernel.org/r/[email protected] open here
Signed-off-by Ingo Molnar <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 include/linux/delayacct.h |    8 ++++----
 kernel/delayacct.c        |   42 ++++++++++++++++++++++++++----------------
 kernel/sched/core.c       |    6 +++---
 3 files changed, 33 insertions(+), 23 deletions(-)
include/linux/delayacct.h +4 -4
@@ -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
 		__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(st
 {}
 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)
kernel/delayacct.c +26 -16

67 lines not on this page · raw message

kernel/sched/core.c +3 -3
@@ -2046,7 +2046,7 @@ try_to_wake_up(struct task_struct *p, un
 	p->state = TASK_WAKING;
 
 	if (p->in_iowait) {
-		delayacct_blkio_end();
+		delayacct_blkio_end(p);
 		atomic_dec(&task_rq(p)->nr_iowait);
 	}
 

@@ -2059,7 +2059,7 @@ try_to_wake_up(struct task_struct *p, un
 #else /* CONFIG_SMP */
 
 	if (p->in_iowait) {
-		delayacct_blkio_end();
+		delayacct_blkio_end(p);
 		atomic_dec(&task_rq(p)->nr_iowait);
 	}
 

@@ -2112,7 +2112,7 @@ static void try_to_wake_up_local(struct
 
 	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);

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/delayacct-account-blkio-completion-on-the-correct-task.patch