linux-kernel - Re: [PATCH 0/6 v7] sched/fair: Add push task mecansim and hadle more EAS cases

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Message-ID: <CAKfTPtDY9rN=g5+tkmXVLJZdFGLCkb3-HkpqoL+ZzYUTTjQEpg@mail.gmail.com>
Date: Mon, 1 Dec 2025 18:48:46 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Christian Loehle <christian.loehle@....com>
Cc: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com, 
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com, 
	mgorman@...e.de, vschneid@...hat.com, linux-kernel@...r.kernel.org, 
	pierre.gondois@....com, kprateek.nayak@....com, qyousef@...alina.io, 
	hongyan.xia2@....com, luis.machado@....com
Subject: Re: [PATCH 0/6 v7] sched/fair: Add push task mecansim and hadle more
 EAS cases

On Mon, 1 Dec 2025 at 14:31, Christian Loehle <christian.loehle@....com> wrote:
>
> On 12/1/25 09:13, Vincent Guittot wrote:
> > This is a subset of [1] (sched/fair: Rework EAS to handle more cases)
> >
> > [1] https://lore.kernel.org/all/20250314163614.1356125-1-vincent.guittot@linaro.org/
> >
> > The current Energy Aware Scheduler has some known limitations which have
> > became more and more visible with features like uclamp as an example. This
> > serie tries to fix some of those issues:
> > - tasks stacked on the same CPU of a PD
> > - tasks stuck on the wrong CPU.
> >
> > Patch 1 fixes the case where a CPU is wrongly classified as overloaded
> > whereas it is capped to a lower compute capacity. This wrong classification
> > can prevent periodic load balancer to select a group_misfit_task CPU
> > because group_overloaded has higher priority.
> >
> > Patch 2 removes the need of testing uclamp_min in cpu_overutilized to
> > trigger the active migration of a task on another CPU.
> >
> > Patch 3 prepares select_task_rq_fair() to be called without TTWU, Fork or
> > Exec flags when we just want to look for a possible better CPU.
> >
> > Patch 4 adds push call back mecanism to fair scheduler but doesn't enable
> > it.
> >
> > Patch 5 enable has_idle_core for !SMP system to track if there may be an
> > idle CPU in the LLC.
> >
> > Patch 6 adds some conditions to enable pushing runnable tasks for EAS:
> > - when a task is stuck on a CPU and the system is not overutilized.
> > - if there is a possible idle CPU when the system is overutilized.
> >
> > More tests results will come later as I wanted to send the pachtset before
> > LPC.
> >
> > Tbench  on dragonboard rb5
> > schedutil and EAS enabled
> >
> > # process     tip                   +patchset
> > 1              29.1(+/-4.1%)        124.7(+/-12.3%) +329%
> > 2              60.0(+/-0.9%)        216.1(+/- 7.9%) +260%
> > 4             255.8(+/-1.9%)        421.4(+/- 2.0%)  +65%
> > 8            1317.3(+/-4.6%)       1396.1(+/- 3.0%)   +6%
> > 16            958.2(+/-4.6%)        979.6(+/- 2.0%)   +2%
>
> Just so I understand, there's no uclamp in the workload here?

Yes, no uclamp

> Could you expand on the workload a little, what were the parameters/settings?

for g in 1 2 4 8 16; do
for i in {0..8}; do
sync
sleep 3.777
tbench -t 10 $g
done
done

> So the significant increase is really only for nr_proc < nr_cpus, with the

yes

> observed throughput increase it'll probably be something like "always running
> on little CPUs" vs "always running on big CPUs", is that what's happening?

I have looked at the details. These results are part of the bench that
I'm running with hackbench but It's most probably come from migrating
task on a better cpu

> Also shouldn't tbench still have plenty of wakeup events? It issues plenty of
> TCP anyway.

Yes


>
> >
> > Hackbench didn't show any difference
> >
> >
> > Vincent Guittot (6):
> >   sched/fair: Filter false overloaded_group case for EAS
> >   sched/fair: Update overutilized detection
> >   sched/fair: Prepare select_task_rq_fair() to be called for new cases
> >   sched/fair: Add push task mechanism for fair
> >   sched/fair: Enable idle core tracking for !SMT
> >   sched/fair: Add EAS and idle cpu push trigger
> >
> >  kernel/sched/fair.c     | 350 +++++++++++++++++++++++++++++++++++-----
> >  kernel/sched/sched.h    |  46 ++++--
> >  kernel/sched/topology.c |   3 +
> >  3 files changed, 346 insertions(+), 53 deletions(-)
> >
>