linux-kernel - Re: [BUG] hotplug cpus on ia64

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Date:	Wed, 4 Jun 2008 08:50:20 -0500
From:	Dimitri Sivanich <sivanich@....com>
To:	Cliff Wickman <cpw@....com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG] hotplug cpus on ia64

On Tue, Jun 03, 2008 at 05:17:59PM -0500, Cliff Wickman wrote:
> 
> On Fri, May 30, 2008 at 03:36:54PM +0200, Peter Zijlstra wrote:
> > On Thu, 2008-05-29 at 11:32 -0500, Cliff Wickman wrote:
> > > I put in counters and see that schedule() is never again entered by cpu 17
> > > after it is downed the 3rd time.
> > > (it is entered after being up'd the first two times)
> > > 
> > > The kstopmachine thread is bound to cpu 17 by __stop_machine_run()'s call
> > > to kthread_bind().
> > > 
> > > A cpu does not schedule after being downed, of course.  But it does again
> > > after being up'd.  
> > > Why would the second up be different?  Following it, if the cpu is
> > > downed it never schedules again.
> > > 
> > > If I always bind kstopmachine to cpu 0 the problem disappears.
> > 
> > does:
> > 
> > echo -1 > /proc/sys/kernel/sched_rt_runtime_us
> > 
> > fix the problem?
> 
> Yes! It does. 
> 
> Dimitri Sivanich has run into what looks like a similar problem.
> Hope the above workaround is a good clue to its solution.

This fixes the problem I was seeing as well.
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