linux-kernel - Re: [PATCH 0/4] sched: The newidle balance regression

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Message-ID: <20251114093711.GG3245006@noisy.programming.kicks-ass.net>
Date: Fri, 14 Nov 2025 10:37:11 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Chris Mason <clm@...a.com>
Cc: Joseph Salisbury <joseph.salisbury@...cle.com>,
	Adam Li <adamli@...amperecomputing.com>,
	Hazem Mohamed Abuelfotoh <abuehaze@...zon.com>,
	Josh Don <joshdon@...gle.com>, 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
Subject: Re: [PATCH 0/4] sched: The newidle balance regression

On Wed, Nov 12, 2025 at 04:59:45PM -0500, Chris Mason wrote:
> On 11/7/25 11:06 AM, Peter Zijlstra wrote:
> > Hi!
> > 
> > So most of you ran into Chris' commit 155213a2aed4 ("sched/fair: Bump
> > sd->max_newidle_lb_cost when newidle balance fails") [*]
> > 
> > And I posted a patch with a few alternative options. And while I've heard back
> > from a number of you, indicating that NI_TARGET (the effective revert) works
> > for you. Not many tested TARGET+RANDOM (thanks Adam!).
> > 
> > In my limited schbench testing that combination isn't horrible, and per Adam
> > that combination also doesn't suck for him. Chris, could you please see what
> > this does for your machines with your actual workload?
> > 
> > Anyway, here are a few patches that basically do the revert and introduce the
> > proportional newidle balance -- the NI_TARGET+NI_RANDOM equivalent.
> > 
> > Also at:
> > 
> >   git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git sched/newidle
> > 
> > Please all, give it a whirl. Hopefully I didn't wreck it, its Friday after all :-)
> > 
> > [*] https://lkml.kernel.org/r/006c9df2-b691-47f1-82e6-e233c3f91faf@oracle.com 
> 
> This is working well for my original benchmark.  Focusing on newidle
> balance schedstat counters (10 second interval):
> 
> Linus:
> lb_balance_newly_idle              22854
> 
> Mason-revert:
> lb_balance_newly_idle            2334059
> 
> Peter:
> lb_balance_newly_idle              75271
> 
> The rest of the schbench numbers look good too.

Sweet!