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

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Message-ID: <20260127084412.GV171111@noisy.programming.kicks-ass.net>
Date: Tue, 27 Jan 2026 09:44:12 +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 Sun, Jan 25, 2026 at 12:22:21PM +0000, Mohamed Abuelfotoh, Hazem wrote:
> I can confirm that we are seeing a 4-11% performance regression in v6.12.66
> on multiple benchmarks running on c7a.4xlarge AWS EC2 instances that are
> powered by AMD EPYC 9R14-series CPU (code-named Genoa) and c7i.4xlarge which
> is powered by 4th-Generation Intel Xeon Scalable processor (code-named
> Sapphire Rapids).

For those not speaking Amazon; what actual system setup is that Xeon? Is
that single socket or multi-socket?

Going by the name, the 4x would suggest a quad-socket Xeon, which are
somewhat beastly, but if I google this 'c7i.4xlarge' identifier, I get a
puny single socket 16cpu thing.

What is it?