Re: [PATCH v2 00/10] sched: Flatten the pick

[Peter Zijlstra]

On Tue, May 12, 2026 at 08:32:12PM +0200, Vincent Guittot wrote:
> On Tue, 12 May 2026 at 20:25, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> >
> > On Tue, May 12, 2026 at 08:24:39PM +0200, Peter Zijlstra wrote:
> > > On Tue, May 12, 2026 at 11:20:40AM +0200, Peter Zijlstra wrote:
> > > > On Tue, May 12, 2026 at 10:42:33AM +0200, Vincent Guittot wrote:
> > > >
> > > > >
> > > > > I haven't reviewed the patches yet but I ran some tests with it while
> > > > > testing sched latency related changes for short slice wakeup
> > > > > preemption. I have some large hackbench regressions with this series
> > > > > on HMP system with and without EAS. those figures are unexpected
> > > > > because the benchs run on root cfs
> > > > >
> > > > > One example with hackbench 8 groups thread pipe
> > > > > tip/sched/core  tip/sched/core          +this patchset          +this patchset
> > > > > slice 2.8ms     16ms                    2.8ms                   16ms
> > > > > dragonboard rb5 with EAS
> > > > > 0,748(+/-4,6%)  0,621(+/-3.6%) +17%     1,915(+/-7.9%) -156%
> > > > > 0,689(+/- 9.1%) +8%
> > > > >
> > > > > radxa orion6 HMP without EAS
> > > > > 0,588(+/-5.8%)  0,677(+/-5.9%) -15%     1,505(+/-10%) -156%
> > > > > 1,071(+/-5.9%) -82%
> > > > >
> > > > > Increasing the slice partly removes regressions but tis is surprising
> > > > > because the bench runs at root cfs and I thought that results will not
> > > > > change in such a case
> > > > >
> > > > > I will review the patchset and try to get what is going wrong
> > > >
> > > > Yeah, that is unexpected. Let me go have another look too.
> > >
> > > So I can reproduce even without the last patch applied. I suspect it is
> > > in the cgroup mode patches somewhere. My first suspect is that concur
> > > mode thing doing bad things to track the 'global' nr_running thing.
> >
> > Argh, n/m PEBKAC. I'll try this again in the morning :/
> 
> Reverting the last patch is enough to recover performance

Yeah, I was on a fail-streak yesterday. I forgot to copy the kernel
image before reboot ...

Lets see if today is better :-)