linux-kernel - Re: [RFC PATCH] sched/fair: Make tg->load

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Message-ID: <20230412120736.GD628377@hirez.programming.kicks-ass.net>
Date:   Wed, 12 Apr 2023 14:07:36 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Daniel Jordan <daniel.m.jordan@...cle.com>
Cc:     Aaron Lu <aaron.lu@...el.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ingo Molnar <mingo@...hat.com>,
        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>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Tim Chen <tim.c.chen@...el.com>,
        Nitin Tekchandani <nitin.tekchandani@...el.com>,
        Waiman Long <longman@...hat.com>,
        Yu Chen <yu.c.chen@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] sched/fair: Make tg->load_avg per node

On Thu, Mar 30, 2023 at 01:45:57PM -0400, Daniel Jordan wrote:

> The topology of my machine is different from yours, but it's the biggest
> I have, and I'm assuming cpu count is more important than topology when
> reproducing the remote accesses.  I also tried on

Core count definitely matters some, but the thing that really hurts is
the cross-node (and cross-cache, which for intel happens to be the same
set) atomics.

I suppose the thing to measure is where this cost rises most sharply on
the AMD platforms -- is that cross LLC or cross Node?

I mean, setting up the split at boot time is fairly straight forward and
we could equally well split at LLC.