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Subject: Re: [patch 3/3] sched: Use local_irq_save_nmi() in cpu_clock()
From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: mingo@elte.hu, David Miller <davem@davemloft.net>, acme@redhat.com,
       paulus@samba.org, Mike Galbraith <efault@gmx.de>,
       Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
       sparclinux@vger.kernel.org, linux-arch@vger.kernel.org
In-Reply-To: <20100407112707.GA5143@nowhere>
References: <20100406132807.698467930@chello.nl>
	 <20100406133141.039454288@chello.nl>  <20100407112707.GA5143@nowhere>
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Date: Wed, 07 Apr 2010 13:31:34 +0200
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On Wed, 2010-04-07 at 13:27 +0200, Frederic Weisbecker wrote:
> On Tue, Apr 06, 2010 at 03:28:10PM +0200, Peter Zijlstra wrote:
> > Since we can call cpu_clock() from NMI context fix up the IRQ
> > disabling to conform to the new rules.
> > 
> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> > ---
> >  kernel/sched_clock.c |    4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > Index: linux-2.6/kernel/sched_clock.c
> > ===================================================================
> > --- linux-2.6.orig/kernel/sched_clock.c
> > +++ linux-2.6/kernel/sched_clock.c
> > @@ -241,9 +241,9 @@ unsigned long long cpu_clock(int cpu)
> >  	unsigned long long clock;
> >  	unsigned long flags;
> >  
> > -	local_irq_save(flags);
> > +	local_irq_save_nmi(flags);
> >  	clock = sched_clock_cpu(cpu);
> > -	local_irq_restore(flags);
> > +	local_irq_restore_nmi(flags);
> >  
> >  	return clock;
> >  }
> 
> 
> That seem to add a small overhead in various places.
> Do we want to make local_irq_save_nmi == local_irq_save
> for archs that have native nmi?

That is already so, see 1/3.