linux-kernel - Re: [PATCH v2] sched/fair: Prefer cache locality for EAS wakeup

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Message-ID: <548ADCD4-7726-460C-A645-8BF74ADBCB06@os.amperecomputing.com>
Date: Thu, 13 Nov 2025 00:03:33 +0000
From: Shubhang Kaushik Prasanna Kumar <shkaushik@...erecomputing.com>
To: "vineethr@...ux.ibm.com" <vineethr@...ux.ibm.com>
CC: Shijie Huang <Shijie.Huang@...erecomputing.com>, Adam Li
	<adam.li@...erecomputing.com>, "bsegall@...gle.com" <bsegall@...gle.com>,
	"cl@...two.org" <cl@...two.org>, "dietmar.eggemann@....com"
	<dietmar.eggemann@....com>, "juri.lelli@...hat.com" <juri.lelli@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mgorman@...e.de" <mgorman@...e.de>, "mingo@...hat.com" <mingo@...hat.com>,
	"peterz@...radead.org" <peterz@...radead.org>, "rostedt@...dmis.org"
	<rostedt@...dmis.org>, "sh@...two.org" <sh@...two.org>, Shubhang Kaushik OS
	<shubhang@...amperecomputing.com>, "vincent.guittot@...aro.org"
	<vincent.guittot@...aro.org>, "vschneid@...hat.com" <vschneid@...hat.com>,
	Frank Wang <zwang@...erecomputing.com>
Subject: Re: [PATCH v2] sched/fair: Prefer cache locality for EAS wakeup

Hi Vineeth,

	> Is cache locality prioritized even over idle CPU availability?

I had assumed that the fast path prioritizes cache locality over idle CPU selection. However, our performance measurements indicate that, in this specific scenario, the trade-off is not worthwhile.
The data shows that prioritizing the busy, `cache-hot` core leads to performance regressions and an overload on wakeup. Which  means an overhead of staying on the busy core outweighs the cost of migrating to an idle core.
In development, I am trying an alternative approach to benefit from cache locality in this path.

Regards,
Shubhang Kaushik