Messages in this thread | | | Date | Tue, 8 Sep 2015 15:45:53 +0900 | From | Byungchul Park <> | Subject | Re: [PATCH] sched: fix lose fair sleeper bonus in switch_to_fair() |
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On Tue, Sep 08, 2015 at 02:23:56PM +0800, Wanpeng Li wrote: > On 9/8/15 2:14 PM, Byungchul Park wrote: > >On Tue, Sep 08, 2015 at 01:38:08PM +0800, Wanpeng Li wrote: > >>On 9/8/15 1:28 PM, Byungchul Park wrote: > >>>On Tue, Sep 08, 2015 at 11:46:01AM +0800, Wanpeng Li wrote: > >>>>On 9/7/15 10:02 PM, Peter Zijlstra wrote: > >>>>>Please always Cc at least the person who wrote the lines you modify. > >>>>> > >>>>>On Mon, Sep 07, 2015 at 05:45:20PM +0800, Wanpeng Li wrote: > >>>>>>The sleeper task will be normalized when moved from fair_sched_class, in > >>>>>>order that vruntime will be adjusted either the task is running or sleeping > >>>>>>when moved back. The nomalization in switch_to_fair for sleep task will > >>>>>>result in lose fair sleeper bonus in place_entity() once the vruntime - > >>>>>>cfs_rq->min_vruntime is big when moved from fair_sched_class. > >>>>>> > >>>>>>This patch fix it by adjusting vruntime just during migrating as original > >>>>>>codes since the vruntime of the task has usually NOT been normalized in > >>>>>>this case. > >>>>>Sorry, I cannot follow that at all. Maybe its me being sleep deprived, > >>>>>but could you try that again? > >>>>When changing away from the fair class while sleeping, relative > >>>>vruntime is calculated to handle the case sleep when moved from > >>>>fair_sched_class and running when moved to fair_sched_class. The > >>>i don't think relative vruntime is calculated to handle the special case > >>>you mentioned. i think the calculation is necessary for all cases detaching > >>Please refer why the relative vruntime caculation is introduced to > >>switched_from_fair(): https://lkml.org/lkml/2011/1/17/129 > >hello, > > > >it is just a bug caused by not calculating a relative vruntime when > >detached a task from cfs_rq, which is necessary though. > > Refer to Peterz's comments: > > | There is also a case where it was moved from fair_sched_class when it > | was in a blocked state and moved back while it is running. > > > > >>>a task from a cfs_rq. > >>> > >>>>absolute vruntime will be calculated in enqueue_entity() either the > >>>>task is running or sleeping when moved back. The fair sleeper bonus > >>>i think absolute vruntime is calculated in enqueue_entuty() only when the > >>>task is on rq. therefore in the case that the task is not on rq, > >>>switched_to_fair() has to calculate the absolute vruntime instread. > >>Absolute vruntime is caculated in place_entity() which is called by > >>enqueue_entity() for DEQUEUE_SLEEP task. > >as you may know, place_entity() is not for calculating an absolute > >vruntime though.. anyway the important thing here is that, when a > >sleeping task is moved back to fair class, enqueue_entity() for > >DEQUEUE_SLEEP task won't be called. > > The enqueue_entity() for DEQUEUE_SLEEP task will be called when the > task is wake up.
now, i see what it means "enqueue_entity() for DEQUEUE_SLEEP task".
> > Regards, > Wanpeng Li > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
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