Messages in this thread | | | From | David Laight <> | Subject | RE: Scheduling tasks on idle cpu | Date | Thu, 14 Apr 2022 08:35:07 +0000 |
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From: Vincent Guittot > Sent: 14 April 2022 08:54 > > 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
Is there a way to dump the kernel NUMA/LLC tables? This might be relevant (with everything idle): # cat /proc/schedstat version 15 timestamp 5388989193 cpu0 0 0 0 0 0 0 117226041384582 250531565354 206276873 domain0 00,00100001 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 domain1 55,55555555 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 domain2 ff,ffffffff 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 cpu1 0 0 0 0 0 0 115978661288718 251736933814 297093280 domain0 00,00200002 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 domain1 aa,aaaaaaaa 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 domain2 ff,ffffffff 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 All the later cpu follow the same pattern (domain0 shifts left every cpu).
I could interpret that as meaning: cpu n and (n + 20) are the hyperthreading pairs. Even numbered cpu are on one chip, odd numbered on the other.
The migrate was: 34533 [017]: sched_migrate_task: pid=34512 prio=120 orig_cpu=14 dest_cpu=17 All the idle cpu were even.
> David can rerun is use case after disabling sched_feat(SIS_PROP)
How would I do that?
David
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