linux-kernel - Re: [PATCH RFC/RFT] sched/fair: Improve the behavior of sync flag

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Message-ID: <1503818196.7566.82.camel@gmx.de>
Date:   Sun, 27 Aug 2017 09:16:36 +0200
From:   Mike Galbraith <efault@....de>
To:     Joel Fernandes <joelaf@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Josef Bacik <jbacik@...com>, Juri Lelli <Juri.Lelli@....com>,
        Brendan Jackman <brendan.jackman@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Rik van Riel <riel@...hat.com>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH RFC/RFT] sched/fair: Improve the behavior of sync flag

On Sat, 2017-08-26 at 23:39 -0700, Joel Fernandes wrote:
> 
> > P.S. to get the most bang for your synchronous buck, you want a
> > preemptive wakeup.. but that butts heads with the fair engine.
> >
> 
> By preemptive wake up I guess you mean the waker would give up its
> time slice and let the wakee use it? That's a cool idea but I agree it
> would be against the fair task behavior.

No, I meant a preemption, that being the cheapest switch.  Any mucking
about with vruntime is a non-starter (NAK bait), making guaranteed
preemption a non-starter.

	-Mike