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

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Message-ID: <8b8b3b52-be6b-3978-4a4c-b72323cf2bd8@amd.com>
Date:   Fri, 2 Jun 2023 14:49:56 +0530
From:   K Prateek Nayak <kprateek.nayak@....com>
To:     Peter Zijlstra <peterz@...radead.org>
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()

Hello Peter,

On 6/2/2023 12:24 PM, Peter Zijlstra wrote:
> 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,

I agree that is much cleaner but workloads rarely like clean solutions
nowadays :)

> 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.

Queued some tests on NPS2/4, and also with the "nr = 4" heuristic.
I'll share the results once they finish.
--
Thanks and Regards,
Prateek