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

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Message-ID: <20260204140552.GF3016024@noisy.programming.kicks-ass.net>
Date: Wed, 4 Feb 2026 15:05:52 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: "Mohamed Abuelfotoh, Hazem" <abuehaze@...zon.com>
Cc: Mario Roy <marioeroy@...il.com>, Chris Mason <clm@...a.com>,
	Joseph Salisbury <joseph.salisbury@...cle.com>,
	Adam Li <adamli@...amperecomputing.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 4/4] sched/fair: Proportional newidle balance

On Wed, Feb 04, 2026 at 01:59:24PM +0000, Mohamed Abuelfotoh, Hazem wrote:
> On 04/02/2026 13:27, Peter Zijlstra wrote:
> > CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
> > 
> > 
> > 
> > On Wed, Feb 04, 2026 at 12:45:41PM +0000, Mohamed Abuelfotoh, Hazem wrote:
> > 
> > > Version           | Benchmark name   | SUT EC2 Instance| diff %
> > > v6.12.66          | postgresql       | c7a.4xlarge     | -4.0%
> > > v6.12.66          | nginx_lb         | c7a.4xlarge     | -5.0%
> > > v6.12.66          | memcached        | c7a.4xlarge     | -11.0%
> > > v6.12.66_proposed | postgresql       | c7a.4xlarge     | -4.0%
> > > v6.12.66_proposed | nginx_lb         | c7a.4xlarge     | -5.0%
> > > v6.12.66_proposed | memcached        | c7a.4xlarge     | -13.0%
> > 
> > *sigh*, that actually made it worse for memcached :/ I'm not familiar
> > with the memcached benchmark, is this something I can run on a single
> > machine, or does it require high speed networking and 2 machines?
> 
> Yup that's true it's slightly worse on memcached with the proposed fix:( The
> memcached benchmark is kind of multi-layer test where you need at at least 2
> client machines and 1 server machine and 1 machine as a test coordinator.
> The server VM is able to achieve 12.5 Gbps of network bandwidth and the
> client each one is able to achieve 30 Gbps so I think it will be tricky and
> likely impossible to reproduce this on a single machine.

Urgh, yeah, while I have multiple machines, not two of them are the same
and I can only offer 1 Gbps of networking, that's not going to keep
anything busy.

> I will try to
> come-up with standalone reproduction steps that can be used to investigate
> this memcached regression. Meanwhile we will share the fio regression
> reproduction steps that I mentioned in my previous update. This should be
> much simpler in steps and can be done on a single machine.

Thanks! I have a few machines with a 'spare' nvme drive to run things
on, hopefully that is sufficient.