linux-kernel - Re: [RFC PATCH 1/2] sched: Rate limit migrations to 1 per 2ms per task

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Message-ID: <20230906094744.GE38741@noisy.programming.kicks-ass.net>
Date:   Wed, 6 Sep 2023 11:47:44 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Swapnil Sapkal <Swapnil.Sapkal@....com>,
        Aaron Lu <aaron.lu@...el.com>,
        Julien Desfossez <jdesfossez@...italocean.com>, x86@...nel.org
Subject: Re: [RFC PATCH 1/2] sched: Rate limit migrations to 1 per 2ms per
 task

On Tue, Sep 05, 2023 at 03:44:57PM -0700, Tim Chen wrote:

> Reading up on sched_clock() documentation and seems like it should 
> indeed be monotonic.

It tries very hard to be monotonic but cannot guarantee. The moment TSC
is found unstable it's too late to fix up everything.