linux-kernel - Re: [patch 3/3] sched: Use local_irq_save_nmi() in cpu

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Date:	Wed, 7 Apr 2010 13:44:14 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...e.hu, David Miller <davem@...emloft.net>, acme@...hat.com,
	paulus@...ba.org, Mike Galbraith <efault@....de>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [patch 3/3] sched: Use local_irq_save_nmi() in cpu_clock()

On Wed, Apr 07, 2010 at 01:31:34PM +0200, Peter Zijlstra wrote:
> 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@...llo.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.


Ah you're right.

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