linux-kernel - Re: [RFC PATCH v4 00/19] Core scheduling v4

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Message-ID: <CAERHkrscBs8WoHSGtnH9mVsN3thfkE0CCQYPRE=XFUWWkQooQQ@mail.gmail.com>
Date:   Wed, 26 Feb 2020 15:21:53 +0800
From:   Aubrey Li <aubrey.intel@...il.com>
To:     Vineeth Remanan Pillai <vpillai@...italocean.com>
Cc:     Aaron Lu <aaron.lwe@...il.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul Turner <pjt@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Dario Faggioli <dfaggioli@...e.com>,
        Frédéric Weisbecker <fweisbec@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Kerr <kerrnel@...gle.com>, Phil Auld <pauld@...hat.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 v4 00/19] Core scheduling v4

On Wed, Feb 26, 2020 at 4:51 AM Vineeth Remanan Pillai
<vpillai@...italocean.com> wrote:
>
> I have a quick patch
> which might fix this. The idea is that, we allow migration if p's
> hierarchical load or estimated utilization is more than dest_rq->curr.
> While thinking about this fix, I noticed that we are not holding the
> dest_rq lock for any of the migration patches. Migration patches would
> probably need a rework. Attaching my patch down, but it also does not
> take the dest_rq lock. I have also added a case of dest_core being
> forced_idle. I think that would be an opportunity to migrate. Ideally
> we should check if the forced idle task has the same cookie as p.
>
> https://gist.github.com/vineethrp/887743608f42a6ce96bf7847b5b119ae
>

Hi Vineeth,

Thanks for the quick fix. I guess this patch should work for Aaron's case
because it almost removed the cookie checking here. Some comments
below:

+ if (rq->core->core_forceidle)
+         return true;

We check cookie match during load balance to avoid two different
cookie tasks on the same core. If one cpu is forced idle, its sibling should
be running a non-idle task, not sure why we can return true directly here.
And if we need to check cookie, with this forced idle case, why it's special
to be picked up?

+ if (task_h_load(p) > task_h_load(rq->curr))
+         return true;
+ if (task_util_est(p) > task_util_est(rq->curr))
+         return true;

These two need to exclude rq->curr == rq->idle case?
otherwise idle balance always return true?

Thanks,
-Aubrey