Date: Mon, 7 Nov 2016 13:54:12 -0600 (CST)
From: Christoph Lameter <cl@linux.com>
To: Steven Rostedt <rostedt@goodmis.org>
cc: Daniel Bristot de Oliveira <bristot@redhat.com>,
        Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        linux-rt-users <linux-rt-users@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] sched/rt: RT_RUNTIME_GREED sched feature
In-Reply-To: <20161107144738.4811a5dd@gandalf.local.home>
Message-ID: <alpine.DEB.2.20.1611071353440.19543@east.gentwo.org>
References: <fa5b1b55d8934c6a0e02e04a7ad6afdf4012c2e0.1478506194.git.bristot@redhat.com> <alpine.DEB.2.20.1611071054320.17809@east.gentwo.org> <20161107133207.4282de69@gandalf.local.home> <alpine.DEB.2.20.1611071328470.19249@east.gentwo.org>
 <20161107144738.4811a5dd@gandalf.local.home>
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On Mon, 7 Nov 2016, Steven Rostedt wrote:

> On Mon, 7 Nov 2016 13:30:15 -0600 (CST)
> Christoph Lameter <cl@linux.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?