linux-kernel - Re: [PATCH] sched/fair: Prefer cache-hot prev

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Message-ID:
 <MW6PR01MB8368D20CAB164517819E9C8CF5F8A@MW6PR01MB8368.prod.exchangelabs.com>
Date: Fri, 31 Oct 2025 16:45:55 +0000
From: Shubhang Kaushik OS <Shubhang@...amperecomputing.com>
To: Dietmar Eggemann <dietmar.eggemann@....com>, Shubhang <sh@...two.org>,
	Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Juri
 Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>,
	Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel
 Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>, Shijie
 Huang <Shijie.Huang@...erecomputing.com>, Frank Wang
	<zwang@...erecomputing.com>
CC: Christopher Lameter <cl@...two.org>, Adam Li
	<adam.li@...erecomputing.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched/fair: Prefer cache-hot prev_cpu for wakeup

Sorry about the confusion. Upon CONFIG_SCHED_CLUSTER enabled, we have the two distinct levels of
scheduling domains : the 2-CPU groups in domain0 and the 80-CPU group in domain1. Yes, I would have to avoid EAS approach altogether
as they require asymmetric CPUs.

Regards,
Shubhang



________________________________________
From: Dietmar Eggemann <dietmar.eggemann@....com>
Sent: Friday, October 31, 2025 4:32 AM
To: Shubhang; Shubhang Kaushik OS; Ingo Molnar; Peter Zijlstra; Juri Lelli; Vincent Guittot; Steven Rostedt; Ben Segall; Mel Gorman; Valentin Schneider; Shijie Huang; Frank Wang
Cc: Christopher Lameter; Adam Li; linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/fair: Prefer cache-hot prev_cpu for wakeup

On 30.10.25 17:35, Shubhang wrote:
> The system is an 80 core Ampere Altra with a two-level
> sched domain topology. The MC domain contains all 80 cores.

Ah OK. So I assume the other SD is CLS with 2 CPUs?

Does this mean you guys have recently changed the sched topology on this
thing? I still remember setups with 2 CPUs in MC and 80 CPUs on PKG.

If this is the case, is:

db1e59483dfd - topology: make core_mask include at least
cluster_siblings (2022-04-20 Darren Hart)

still needed in this case?

> I agree that placing the condition earlier in `select_idle_sibling()`>
aligns better with convention. I will move the check (EAS Aware) to the
> top of the function and submit a v2 patch.
I can't imagine that you run EAS on this machine? It needs heterogeneous
CPUs which you shouldn't have. Looks like that Christian L. was asking
you already on your v2.

[...]