linux-kernel - Re: [PATCH v15 04/13] task_isolation: add initial support

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Message-ID: <ee883e4b-6f5a-6025-e505-76c6b8db4e76@mellanox.com>
Date:   Fri, 2 Sep 2016 10:03:52 -0400
From:   Chris Metcalf <cmetcalf@...lanox.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Gilad Ben Yossef <giladb@...lanox.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Rik van Riel <riel@...hat.com>, Tejun Heo <tj@...nel.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Christoph Lameter <cl@...ux.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...capital.net>,
        Michal Hocko <mhocko@...e.com>, <linux-mm@...ck.org>,
        <linux-doc@...r.kernel.org>, <linux-api@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v15 04/13] task_isolation: add initial support

On 9/1/2016 6:06 AM, Peter Zijlstra wrote:
> On Tue, Aug 30, 2016 at 11:32:16AM -0400, Chris Metcalf wrote:
>> On 8/30/2016 3:58 AM, Peter Zijlstra wrote:
>>> What !? I really don't get this, what are you waiting for? Why is
>>> rescheduling making things better.
>> We need to wait for the last dyntick to fire before we can return to
>> userspace.  There are plenty of options as to what we can do in the
>> meanwhile.
> Why not keep your _TIF_TASK_ISOLATION_FOO flag set and re-enter the
> loop?
>
> I really don't see how setting TIF_NEED_RESCHED is helping anything.

Yes, I think I addressed that in an earlier reply to Frederic; and you're right,
I don't think TIF_NEED_RESCHED or schedule() are the way to go.

https://lkml.kernel.org/g/107bd666-dbcf-7fa5-ff9c-f79358899712@mellanox.com

Any thoughts on the question of "just re-enter the loop" vs. schedule_timeout()?

-- 
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com