Messages in this thread | | | Subject | Re: [PATCH] sched: fix lose fair sleeper bonus in switch_to_fair() | From | Wanpeng Li <> | Date | Tue, 8 Sep 2015 14:23:56 +0800 |
| |
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.
Regards, Wanpeng Li
| |