Re: [PATCH] sched/fair: Prefer cache-hot prev_cpu for wakeup

[Shubhang Kaushik OS]

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@xxxxxxx>
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@xxxxxxxxxxxxxxx
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.

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