linux-kernel - Re: [RFC PATCH 3/3] sched: Implement shared wakequeue in CFS

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Date:   Wed, 14 Jun 2023 11:27:07 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Aaron Lu <aaron.lu@...el.com>
Cc:     David Vernet <void@...ifault.com>, linux-kernel@...r.kernel.org,
        mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, rostedt@...dmis.org,
        dietmar.eggemann@....com, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com, joshdon@...gle.com,
        roman.gushchin@...ux.dev, tj@...nel.org, kernel-team@...a.com
Subject: Re: [RFC PATCH 3/3] sched: Implement shared wakequeue in CFS

On Wed, Jun 14, 2023 at 12:35:29PM +0800, Aaron Lu wrote:
> On Tue, Jun 13, 2023 at 10:32:03AM +0200, Peter Zijlstra wrote:
> > 
> > Still gotta read it properly, however:
> > 
> > On Tue, Jun 13, 2023 at 12:20:04AM -0500, David Vernet wrote:
> > > Single-socket | 32-core | 2-CCX | AMD 7950X Zen4
> > > Single-socket | 72-core | 6-CCX | AMD Milan Zen3
> > > Single-socket | 176-core | 11-CCX | 2-CCX per CCD | AMD Bergamo Zen4c
> > 
> > Could you please also benchmark on something Intel that has these stupid
> > large LLCs ?
> > 
> > Because the last time I tried something like this, it came apart real
> > quick. And AMD has these relatively small 8-core LLCs.
> 
> I tested on Intel(R) Xeon(R) Platinum 8358, which has 2 sockets and each
> socket has a single LLC with 32 cores/64threads.

> The lock contention due to the per-LLC swqueue->lock is quite serious:

Yep, that's what I was expecting -- complete meltdown that.