linux-kernel - Re: [RFC PATCH v2 00/17] Core scheduling v2

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Date:   Wed, 8 May 2019 13:49:09 -0400
From:   Julien Desfossez <jdesfossez@...italocean.com>
To:     Aaron Lu <aaron.lu@...ux.alibaba.com>
Cc:     Vineeth Remanan Pillai <vpillai@...italocean.com>,
        Phil Auld <pauld@...hat.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>, mingo@...nel.org,
        tglx@...utronix.de, pjt@...gle.com, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org, subhra.mazumdar@...cle.com,
        fweisbec@...il.com, keescook@...omium.org, kerrnel@...gle.com,
        Aaron Lu <aaron.lwe@...il.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [RFC PATCH v2 00/17] Core scheduling v2

On 08-May-2019 10:30:09 AM, Aaron Lu wrote:
> On Mon, May 06, 2019 at 03:39:37PM -0400, Julien Desfossez wrote:
> > On 29-Apr-2019 11:53:21 AM, Aaron Lu wrote:
> > > This is what I have used to make sure no two unmatched tasks being
> > > scheduled on the same core: (on top of v1, I thinks it's easier to just
> > > show the diff instead of commenting on various places of the patches :-)
> > 
> > We imported this fix in v2 and made some small changes and optimizations
> > (with and without Peter’s fix from https://lkml.org/lkml/2019/4/26/658)
> > and in both cases, the performance problem where the core can end up
> 
> By 'core', do you mean a logical CPU(hyperthread) or the entire core?
No I really meant the entire core.

I’m sorry, I should have added a little bit more context. This relates
to a performance issue we saw in v1 and discussed here:
https://lore.kernel.org/lkml/20190410150116.GI2490@worktop.programming.kicks-ass.net/T/#mb9f1f54a99bac468fc5c55b06a9da306ff48e90b

We proposed a fix that solved this, Peter came up with a better one
(https://lkml.org/lkml/2019/4/26/658), but if we add your isolation fix
as posted above, the same problem reappears. Hope this clarifies your
ask.

I hope that we did not miss anything crucial while integrating your fix
on top of v2 + Peter’s fix. The changes are conceptually similar, but we
refactored it slightly to make the logic clear. Please have a look and
let us know

Thanks,

Julien