linux-kernel - Re: [tip: sched/core] sched/fair: Multi-LLC select_idle

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Date:   Fri, 2 Jun 2023 08:54:38 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     K Prateek Nayak <kprateek.nayak@....com>
Cc:     linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        Tejun Heo <tj@...nel.org>, x86@...nel.org,
        Gautham Shenoy <gautham.shenoy@....com>
Subject: Re: [tip: sched/core] sched/fair: Multi-LLC select_idle_sibling()

On Fri, Jun 02, 2023 at 10:43:37AM +0530, K Prateek Nayak wrote:
> Grouping near-CCX for the offerings that do not have 2CCX per CCD will
> prevent degenration and limit the search scope yes. Here is what I'll
> do, let me check if limiting search scope helps first, and then start
> fiddling with the topology. How does that sound?

So my preference would be the topology based solution, since the search
limit is random magic numbers that happen to work for 'your' machine but
who knows what it'll do for some other poor architecture that happens to
trip this.

That said; verifying the limit helps at all is of course a good start,
because if it doesn't then the topology thing will likely also not help
much.