linux-kernel - Re: [PATCH RFC 1/2] sched: Minimize the idle cpu selection race window.

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Message-ID: <1509519263.12290.30.camel@gmx.de>
Date:   Wed, 01 Nov 2017 07:54:23 +0100
From:   Mike Galbraith <efault@....de>
To:     Atish Patra <atish.patra@...cle.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, joelaf@...gle.com,
        brendan.jackman@....com, jbacik@...com, mingo@...hat.com
Subject: Re: [PATCH RFC 1/2] sched: Minimize the idle cpu selection race
 window.

On Wed, 2017-11-01 at 01:08 -0500, Atish Patra wrote:
> 
> On 10/31/2017 03:48 AM, Mike Galbraith wrote:
> 
> > I played with something ~similar (cmpxchg() idle cpu reservation)
> I had an atomic version earlier as well. Peter's suggestion for per cpu 
> seems to perform slightly better than atomic.

Yeah, no doubt about that.

> Thus, this patch has the per cpu version.
> >   a
> > while back in the context of schbench, and it did help that,
> Do you have the schbench configuration somewhere that I can test? I 
> tried various configurations but did not
> see any improvement or regression.

No, as noted, I didn't save anything.  I watched and fiddled with
several configurations on various sized boxen, doing this/that on top
of the reservation thing to try to improve the "it's 100% about perfect
spread" schbench, but didn't like the pricetag, so tossed the lot over
my shoulder and walked away.

	-Mike