linux-kernel - Re: [PATCH 4/4] sched/fair: Proportional newidle balance

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Message-ID: <20251114093540.GF3245006@noisy.programming.kicks-ass.net>
Date: Fri, 14 Nov 2025 10:35:40 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>
Cc: mingo@...hat.com, juri.lelli@...hat.com, vincent.guittot@...aro.org,
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
	mgorman@...e.de, vschneid@...hat.com, linux-kernel@...r.kernel.org,
	Chris Mason <clm@...a.com>,
	Joseph Salisbury <joseph.salisbury@...cle.com>,
	Adam Li <adamli@...amperecomputing.com>,
	Hazem Mohamed Abuelfotoh <abuehaze@...zon.com>,
	Josh Don <joshdon@...gle.com>
Subject: Re: [PATCH 4/4] sched/fair: Proportional newidle balance

On Wed, Nov 12, 2025 at 09:12:57PM +0530, Shrikanth Hegde wrote:
> 
> 
> On 11/7/25 9:36 PM, Peter Zijlstra wrote:
> > Add a randomized algorithm that runs newidle balancing proportional to
> > its success rate.
> > 
> > This improves schbench significantly:
> > 
> >   6.18-rc4:			2.22 Mrps/s
> >   6.18-rc4+revert:		2.04 Mrps/s
> >   6.18-rc4+revert+random:	2.18 Mrps/S
> > 
> 
> Could you please share the schbench command?
> 
> I see command like "schbench -t 90 -r 30 -i 30" running on 60 core regress.
> Will do more iterations to confirm it (to be sure it is not run/run variation)

This was:

 schbench -L -m 4 -M auto -t 256 -n 0 -r 60 -s 0

from the original thread:

  https://lkml.kernel.org/r/20250626144017.1510594-2-clm@fb.com

> > +	if (sd->newidle_call >= 1024) {
> > +		sd->newidle_ratio = sd->newidle_success;
> > +		sd->newidle_call /= 2;
> > +		sd->newidle_success /= 2;
> > +	}
> 
> Would it be better to >> 1 ? or compiler takes care of it?

I would be very disappointed if our compilers don't do this.