linux-kernel - Re: [PATCH] sched/rt: RT_RUNTIME

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Message-ID: <alpine.DEB.2.20.1611071353440.19543@east.gentwo.org>
Date:   Mon, 7 Nov 2016 13:54:12 -0600 (CST)
From:   Christoph Lameter <cl@...ux.com>
To:     Steven Rostedt <rostedt@...dmis.org>
cc:     Daniel Bristot de Oliveira <bristot@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched/rt: RT_RUNTIME_GREED sched feature

On Mon, 7 Nov 2016, Steven Rostedt wrote:

> On Mon, 7 Nov 2016 13:30:15 -0600 (CST)
> Christoph Lameter <cl@...ux.com> wrote:
>
> > SCHED_RR tasks alternately running on on cpu can cause endless deferral of
> > kworker threads. With the global effect of the OS processing reserved
> > it may be the case that the processor we are executing never gets any
> > time. And if that kworker threads role is releasing a mutex (like the
> > cgroup_lock) then deadlocks can result.
>
> I believe SCHED_RR tasks will still throttle if they use up too much of
> the CPU. But I still don't see how this patch helps your situation.

The kworker thread will be able to make progress? Or am I not reading this
correctly?