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

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Date:	Fri, 20 Oct 2006 00:22:45 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Daniel Walker <dwalker@...sta.com>
CC:	Andi Kleen <ak@...e.de>, 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

Daniel Walker wrote:
> 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 ..

An SMP kernel can boot on UP hardware, in which case I think
num_possible_cpus() will be 1, won't it?

-- 
SUSE Labs, Novell Inc.
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