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

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Message-ID: <20160901100631.GQ10153@twins.programming.kicks-ass.net>
Date:   Thu, 1 Sep 2016 12:06:31 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Chris Metcalf <cmetcalf@...lanox.com>
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 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.