Messages in this thread | | | Subject | Re: [PATCH] sched/fair: Fix the wrong throttled clock time for cfs_rq_clock_task() | From | Xunlei Pang <> | Date | Thu, 12 May 2016 11:36:49 +0800 |
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On 2016/05/11 at 14:49, Peter Zijlstra wrote: > On Tue, May 10, 2016 at 11:19:44AM -0700, bsegall@google.com wrote: >> Xunlei Pang <xlpang@redhat.com> writes: >> >>> Two minor fixes for cfs_rq_clock_task(). >>> 1) If cfs_rq is currently being throttled, we need to subtract the cfs >>> throttled clock time. >>> >>> 2) Make "throttled_clock_task_time" update SMP unrelated. Now UP cases >>> need it as well. >>> >>> Signed-off-by: Xunlei Pang <xlpang@redhat.com> >>> --- >>> kernel/sched/fair.c | 4 +--- >>> 1 file changed, 1 insertion(+), 3 deletions(-) >>> >>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >>> index 1708729e..fb80a12 100644 >>> --- a/kernel/sched/fair.c >>> +++ b/kernel/sched/fair.c >>> @@ -3655,7 +3655,7 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg) >>> static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq) >>> { >>> if (unlikely(cfs_rq->throttle_count)) >>> - return cfs_rq->throttled_clock_task; >>> + return cfs_rq->throttled_clock_task - cfs_rq->throttled_clock_task_time; >>> >>> return rq_clock_task(rq_of(cfs_rq)) - cfs_rq->throttled_clock_task_time; >>> } > The alternative is obviously to do the subtraction in > tg_throttle_down(), were we set ->throttled_clock_task.
It is possible, but throttled_clock_task is a timestamp, I think doing it here is semantically better.
> >>> @@ -3793,13 +3793,11 @@ static int tg_unthrottle_up(struct task_group *tg, void *data) >>> struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)]; >>> >>> cfs_rq->throttle_count--; >>> -#ifdef CONFIG_SMP >>> if (!cfs_rq->throttle_count) { >>> /* adjust cfs_rq_clock_task() */ >>> cfs_rq->throttled_clock_task_time += rq_clock_task(rq) - >>> cfs_rq->throttled_clock_task; >>> } >>> -#endif >>> >>> return 0; >>> } >> [Cc: pjt@google.com] >> >> This looks reasonable to me (at least the first part; I'm not >> certain why the CONFIG_SMP ifdef was put in place). > 64660c864f46 ("sched: Prevent interactions with throttled entities") > > Introduced it, because at that time it was about updating shares, which > is only present on SMP. Then: > > f1b17280efbd ("sched: Maintain runnable averages across throttled periods") > > Added the clock thing inside it, and: > > 82958366cfea ("sched: Replace update_shares weight distribution with per-entity computation") > > took out the shares update and left the clock update, resulting in the > current code. > >
Thanks, Xunlei
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