From mboxrd@z Thu Jan  1 00:00:00 1970
From: Steven Rostedt <rostedt-nx8X9YLhiw1AfugRpC6u6w@public.gmane.org>
Subject: Re: [PATCH 1/2] IB/hfi1: Use preempt_{dis,en}able_nort()
Date: Thu, 5 Oct 2017 11:55:39 -0400
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Cc: Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>,
        Arnaldo Carvalho de Melo <acme-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
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        <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
        Arnaldo Carvalho de Melo <acme-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
        Clark Williams <williams-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
        Dean Luick <dean.luick-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
        Dennis Dalessandro <dennis.dalessandro-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
        Doug Ledford <dledford-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
        Kaike Wan <kaike.wan-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
        Leon Romanovsky <leonro-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>,
        <linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
        Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
        Sebastian Andrzej Siewior <sebastian.siewior-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>,
        Sebastian Sanchez <sebastian.sanchez-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
To: Julia Cartwright <julia-acOepvfBmUk@public.gmane.org>
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On Thu, 5 Oct 2017 10:37:59 -0500
Julia Cartwright <julia-acOepvfBmUk@public.gmane.org> wrote:

> On Thu, Oct 05, 2017 at 05:27:30PM +0200, Thomas Gleixner wrote:
> > On Thu, 5 Oct 2017, Julia Cartwright wrote:  
> > > On Tue, Oct 03, 2017 at 12:49:19PM -0300, Arnaldo Carvalho de Melo wrote:  
> > > > -	preempt_disable();
> > > > +	preempt_disable_nort();
> > > >  	this_cpu_inc(*sc->buffers_allocated);  
> > > 
> > > Have you tried this on RT w/ CONFIG_DEBUG_PREEMPT?  I believe that the
> > > this_cpu_* operations perform a preemption check, which we'd trip.  
> > 
> > Good point. Changing this to migrate_disable() would do the trick.  
> 
> Wouldn't we still trip the preempt check even with migration disabled?
> In another thread I asked the same question: should the preemption
> checks here be converted to migration-checks in RT?

Is it a "preemption check"? Getting a cpu # should only care about
migration. This isn't the same as a rcu_sched check is it? That does
care about preemption.

-- Steve
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