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Date: Mon, 7 Nov 2016 15:00:03 -0500
From: Steven Rostedt <rostedt@goodmis.org>
To: Christoph Lameter <cl@linux.com>
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
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On Mon, 7 Nov 2016 13:54:12 -0600 (CST)
Christoph Lameter <cl@linux.com> wrote:

> 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?
> 

If kworker is SCHED_OTHER, then it will be able to make progress if the
RT tasks are throttled.

What Daniel's patch does, is to turn off throttling of the RT tasks if
there's no other task on the run queue.

-- Steve