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Date: Fri, 23 Sep 2016 14:46:24 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Mike Snitzer <snitzer@redhat.com>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        linux-kernel@vger.kernel.org, dm-devel@redhat.com,
        Joe Thornber <ejt@redhat.com>
Subject: Re: [RFC][PATCH] dm: Remove dm_bufio_cond_resched()
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On Fri, Sep 23, 2016 at 08:42:51AM -0400, Mike Snitzer wrote:
> On Fri, Sep 23 2016 at  8:26am -0400,
> Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > On Fri, Sep 23, 2016 at 02:17:10PM +0200, Mike Galbraith wrote:
> > > On Fri, 2016-09-23 at 10:00 +0200, Thomas Gleixner wrote:
> > > > On Fri, 23 Sep 2016, Peter Zijlstra wrote:
> > > 
> > > > > Is anybody still using PREEMPT_NONE? Most workloads also care about
> > > > > latency to some extend. Lots of code has explicit cond_resched() and
> > > > > doesn't worry.
> > > > 
> > > > Dunno. But I bet there are workloads which love it.
> > > 
> > > SUSE definitely uses it.  I had presumed that was enterprise standard.
> > 
> > Hmm, I thought most distros defaulted to PREEMPT_VOLUNTARY.
> 
> So what is the concensus on this?  Switch dm-bufio's cond_resched calls
> (in peter's patch) to might_sleep()?  Or continue using cond_resched but
> fix cond_resched to do the might_sleep() equivalent if PREEMPT_NONE?

I'd go with the one I posted and look again if ever a performance issue
shows up.