| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <20150908075728.GJ6455@byungchulpark-X58A-UD3R> Date: Tue, 8 Sep 2015 16:57:29 +0900 From: Byungchul Park <byungchul.park@....com> To: Wanpeng Li <wanpeng.li@...mail.com> Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org, yuyang.du@...el.com Subject: Re: [PATCH] sched: fix lose fair sleeper bonus in switch_to_fair() On Tue, Sep 08, 2015 at 03:30:08PM +0800, Wanpeng Li wrote: > On 9/8/15 3:11 PM, Byungchul Park wrote: > >On Tue, Sep 08, 2015 at 02:42:52PM +0800, Wanpeng Li wrote: > >>On 9/8/15 2:32 PM, Byungchul Park wrote: > >>>On Tue, Sep 08, 2015 at 03:14:26PM +0900, 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. > >>>> > >>>>>>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. > >>>you may talk about calling enqueue_entity() when the task is woken up, > >>>not just when it is moved back. right? > >>Exactly. > >> > >>>even if yes, i think place_entity() should not be used directly for > >>>calculating an absolute vruntime. it should be called after non/normalizing > >>>operations. > >>The se->vruntime += cfs_rq->min_vruntime(in your switched_to_fair()) > >>which means that se->vruntime is bigger than cfs_rq->min_vruntime, > >it is not always true since se->vruntime can have a negative value (even > >though it is a unsigned type.. i think it can be another problem) by > >se->vruntime -= cfs_rq->min_vruntime in detach_task_cfs_rq(). > > Yeah, it can be negative. > > > > >>however, fair sleeper bonus is min_vuntime - sysctl_sched_latency/2, > >>which means that max_vruntime() will select the absolute vruntime > >>which is caculated in your switched_to_fair() as the se->vruntime, > >since se->vruntime can have a negative value, max_vruntime() may select > >the fair sleeper bonused value. > > > >by the way, this logic is unchanged by my patch. which part of my patch > >changed this kind of logic? > > However, if se->vruntime -= cfs_rq->min_vruntime is positive, the > behavior is different after your patch. e.g. se->vruntime(the > relative vruntime in switched_to_fair()) < min_vruntime - > sysctl_sched_latency/2 > > before your patch: > > se->vruntime = min_vruntime - sysctl_sched_latency/2 (place_entity()) my patch is based on ff277d4 commit at tip/sched/core. there's no change between before and after. check it please. and this logic seems to be no problem to me. :( > > after your patch: > > se->vruntime += cfs->min_vruntime (switched_to_fair()) > se->vruntime = se->vruntime (place_entity()) > > > Regards, > Wanpeng Li > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists