linux-kernel - Re: [PATCH 0/4] sched: Various reweight

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Message-ID: <20260211104947.GI1395416@noisy.programming.kicks-ass.net>
Date: Wed, 11 Feb 2026 11:49:47 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Doug Smythies <dsmythies@...us.net>,
	K Prateek Nayak <kprateek.nayak@....com>, mingo@...nel.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,
	wangtao554@...wei.com, quzicheng@...wei.com,
	wuyun.abel@...edance.com
Subject: Re: [PATCH 0/4] sched: Various reweight_entity() fixes

On Wed, Feb 11, 2026 at 11:48:33AM +0100, Peter Zijlstra wrote:
> On Wed, Feb 11, 2026 at 10:01:44AM +0100, Peter Zijlstra wrote:
> 
> > > There 2 issues with patch 3
> > > 
> > > *one scale_load_down remains in avg_vruntime
> > > 
> > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > index 25c398ff0d59..3143ae7f07b0 100644
> > > --- a/kernel/sched/fair.c
> > > +++ b/kernel/sched/fair.c
> > > @@ -778,7 +778,7 @@ u64 avg_vruntime(struct cfs_rq *cfs_rq)
> > > 
> > >         if (weight) {
> > >                 if (curr) {
> > > -                       unsigned long w = scale_load_down(curr->load.weight);
> > > +                       unsigned long w =
> > > avg_vruntime_weight(curr->load.weight);
> > > 
> > >                         runtime += entity_key(cfs_rq, curr) * w;
> > >                         weight += w;
> > 
> > AAARGHHH!! Sorry about that, clearly I've not been careful with
> > reshuffling patches :-(
> 
> So with that one fixed; I get (as queue/sched/core of just now):

In case this wasn't clear; this is hackbench as per:

for i in 1 2 5 10 20 40 ; do
  echo -n "${i}: "
  perf stat --null --repeat 10 -- perf bench sched messaging -g $i -t -l 10000 2>&1 | grep "seconds time elapsed"
done


> base:
> 
> 1:            0.25431 +- 0.00226 seconds time elapsed  ( +-  0.89% )
> 2:            0.52522 +- 0.00304 seconds time elapsed  ( +-  0.58% )
> 5:            1.10452 +- 0.00509 seconds time elapsed  ( +-  0.46% )
> 10:           2.00673 +- 0.00761 seconds time elapsed  ( +-  0.38% )
> 20:           3.81795 +- 0.00347 seconds time elapsed  ( +-  0.09% )
> 40:           7.0551  +- 0.0112  seconds time elapsed  ( +-  0.16% )
> 
> +1      patches/peterz-sched-fair-fix-zero_vruntime.patch
> 
> 1:            0.25231 +- 0.00328 seconds time elapsed  ( +-  1.30% )
> 2:            0.52794 +- 0.00337 seconds time elapsed  ( +-  0.64% )
> 5:            1.09336 +- 0.00391 seconds time elapsed  ( +-  0.36% )
> 10:           1.98787 +- 0.00660 seconds time elapsed  ( +-  0.33% )
> 20:           3.75865 +- 0.00782 seconds time elapsed  ( +-  0.21% )
> 40:           7.0208  +- 0.0102  seconds time elapsed  ( +-  0.15% )
> 
> +2      patches/peterz-sched-fair-curb-set_protect_slice.patch
> 
> 1:            0.25421 +- 0.00351 seconds time elapsed  ( +-  1.38% )
> 2:            0.53178 +- 0.00308 seconds time elapsed  ( +-  0.58% )
> 5:            1.09421 +- 0.00462 seconds time elapsed  ( +-  0.42% )
> 10:           1.99843 +- 0.00289 seconds time elapsed  ( +-  0.14% )
> 20:           3.77249 +- 0.00676 seconds time elapsed  ( +-  0.18% )
> 40:           7.0371  +- 0.0143  seconds time elapsed  ( +-  0.20% )
> 
> +3      patches/wang_tao-sched_eevdf-update_se-_vprot_in_reweight_entity.patch
> 
> 1:            0.25141 +- 0.00342 seconds time elapsed  ( +-  1.36% )
> 2:            0.53294 +- 0.00474 seconds time elapsed  ( +-  0.89% )
> 5:            1.10944 +- 0.00447 seconds time elapsed  ( +-  0.40% )
> 10:           2.00012 +- 0.00366 seconds time elapsed  ( +-  0.18% )
> 20:           3.77650 +- 0.00796 seconds time elapsed  ( +-  0.21% )
> 40:           7.0455  +- 0.0145  seconds time elapsed  ( +-  0.21% )
> 
> +4      patches/peter_zijlstra-sched_fair-increase_max_lag_clamping.patch
> 
> 1:            0.25096 +- 0.00415 seconds time elapsed  ( +-  1.65% )
> 2:            0.53635 +- 0.00372 seconds time elapsed  ( +-  0.69% )
> 5:            1.12040 +- 0.00549 seconds time elapsed  ( +-  0.49% )
> 10:           2.00447 +- 0.00518 seconds time elapsed  ( +-  0.26% )
> 20:           3.7682  +- 0.0104  seconds time elapsed  ( +-  0.28% )
> 40:           7.0023  +- 0.0141  seconds time elapsed  ( +-  0.20% )
> 
> +5      patches/peterz-sched-increase-avg-bits.patch
> 
> 1:            0.24866 +- 0.00284 seconds time elapsed  ( +-  1.14% )
> 2:            0.52756 +- 0.00310 seconds time elapsed  ( +-  0.59% )
> 5:            1.09946 +- 0.00643 seconds time elapsed  ( +-  0.58% )
> 10:           1.98256 +- 0.00398 seconds time elapsed  ( +-  0.20% )
> 20:           3.75988 +- 0.00611 seconds time elapsed  ( +-  0.16% )
> 40:           6.9833  +- 0.0113  seconds time elapsed  ( +-  0.16% )
> 
> +6      patches/peterz-sched-revert-reweight-entity-thingy.patch
> 
> 1:            0.25302 +- 0.00285 seconds time elapsed  ( +-  1.13% )
> 2:            0.53040 +- 0.00383 seconds time elapsed  ( +-  0.72% )
> 5:            1.08806 +- 0.00341 seconds time elapsed  ( +-  0.31% )
> 10:           1.97696 +- 0.00592 seconds time elapsed  ( +-  0.30% )
> 20:           3.75393 +- 0.00622 seconds time elapsed  ( +-  0.17% )
> 40:           6.9794  +- 0.0139  seconds time elapsed  ( +-  0.20% )
> 
> 
> Now let me go check on that latency thing from Doug (although hopefully
> that was the same boo-boo).