Messages in this thread | | | From | Vincent Guittot <> | Date | Thu, 14 Apr 2022 09:54:20 +0200 | Subject | Re: Scheduling tasks on idle cpu |
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On Thu, 14 Apr 2022 at 01:57, Qais Yousef <qais.yousef@arm.com> wrote: > > On 04/12/22 11:07, Vincent Guittot wrote: > > On Tue, 12 Apr 2022 at 10:39, David Laight <David.Laight@aculab.com> wrote: > > > Yes I want the CFS scheduler to pick an idle cpu in preference > > > to an active RT one. > > > > When task 34512 wakes up, scheduler checks if prev or this cpu are > > idle which is not the case for you. Then, it compares the load of prev > > and this_cpu and seems to select this_cpu (cpu17). > > > > Once cpu17 selected, it will try to find an idle cpu which shares LLC > > but it seems that the scheduler didn't find one and finally keeps task > > 34512 on this_cpu. > > > > Note that during the next tick, a load balance will be trigger if > > this_cpu still have both RT and task 34512, > > David said there are idle cpus > > " There are two physical cpu with 20 cores each (with hyperthreading). > 16, 18, 34, 36 and 38 were idle. So both 16 and 18 should be on the > same NUMA node. All the others are running the same RT thread code. " > > Except for the possibility of them becoming idle just after the task has woken > up, shouldn't one of them have been picked?
we don't loop on all cpus in the LLC to find an idle one but compute a reasonable number of iteration based on the avg_idle
David can rerun is use case after disabling sched_feat(SIS_PROP)
> > Thanks > > -- > Qais Yousef
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