linux-kernel - Re: + i386-time-avoid-pit-smp-lockups.patch added to -mm tree

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Date:	Thu, 19 Oct 2006 06:57:05 -0700
From:	Daniel Walker <dwalker@...sta.com>
To:	Andi Kleen <ak@...e.de>
Cc:	linux-kernel@...r.kernel.org, johnstul@...ibm.com, mingo@...e.hu,
	tglx@...utronix.de
Subject: Re: + i386-time-avoid-pit-smp-lockups.patch added to -mm tree

On Thu, 2006-10-19 at 15:47 +0200, Andi Kleen wrote:
> On Thursday 19 October 2006 15:44, Daniel Walker wrote:
> > On Wed, 2006-10-11 at 14:26 -0700, akpm@...l.org wrote:
> > 
> > > diff -puN arch/i386/kernel/i8253.c~i386-time-avoid-pit-smp-lockups arch/i386/kernel/i8253.c
> > > --- a/arch/i386/kernel/i8253.c~i386-time-avoid-pit-smp-lockups
> > > +++ a/arch/i386/kernel/i8253.c
> > > @@ -109,7 +109,7 @@ static struct clocksource clocksource_pi
> > >  
> > >  static int __init init_pit_clocksource(void)
> > >  {
> > > -	if (num_possible_cpus() > 4) /* PIT does not scale! */
> > > +	if (num_possible_cpus() > 1) /* PIT does not scale! */
> > >  		return 0;
> > >  
> > 
> > Can we ifdef some code here on CONFIG_SMP . It bugs me that there just
> > dead code laying around on smp systems.
> 
> The optimizer should optimize it all out since num_possible_cpus() is a 0
> constant on UP.

You just mean the if statement above though? I was talking more about
the structure above this called "clocksource_pit" which isn't used on
SMP systems due to this code addition. AFAIK init_pit_clocksource()
could disappear along with the clocksource structure ..

Daniel 

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