Ping On 2016/05/12 at 11:36, Xunlei Pang wrote: > On 2016/05/11 at 14:49, Peter Zijlstra wrote: >> On Tue, May 10, 2016 at 11:19:44AM -0700, bseg...@google.com wrote: >>> Xunlei Pang <xlp...@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 <xlp...@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: p...@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 >