linux-kernel - Re: [PATCH 1/11] Add generic helpers for arch IPI function calls

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Message-ID: <20080425110822.GH14903@elf.ucw.cz>
Date:	Fri, 25 Apr 2008 13:08:22 +0200
From:	Pavel Machek <pavel@....cz>
To:	Mark Lord <lkml@....ca>
Cc:	Jens Axboe <jens.axboe@...cle.com>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org, npiggin@...e.de,
	torvalds@...ux-foundation.org, "Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [PATCH 1/11] Add generic helpers for arch IPI function calls

Hi!

>> Something like this will close the window to right up until the point
>> where the other CPUs have 'almost' called halt().
>>
>> diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
>> index 5398385..94ec9bf 100644
>> --- a/arch/x86/kernel/smp.c
>> +++ b/arch/x86/kernel/smp.c
>> @@ -155,8 +155,9 @@ static void stop_this_cpu(void *dummy)
>>  	/*
>>  	 * Remove this CPU:
>>  	 */
>> -	cpu_clear(smp_processor_id(), cpu_online_map);
>>  	disable_local_APIC();
>> +	cpu_clear(smp_processor_id(), cpu_online_map);
>> +	smp_wmb();
>>  	if (hlt_works(smp_processor_id()))
>>  		for (;;) halt();
>>  	for (;;);
>> @@ -175,6 +176,12 @@ static void native_smp_send_stop(void)
>>   	local_irq_save(flags);
>>  	smp_call_function(stop_this_cpu, NULL, 0, 0);
>> +
>> +	while (cpus_weight(cpu_online_map) > 1) {
>> +		cpu_relax();
>> +		smp_rmb();
>> +	}
>> +
>>  	disable_local_APIC();
>>  	local_irq_restore(flags);
>>  }
> ..
>
> Yup, that looks like it oughta work consistently.
> Now we just need to hear from some of the folks who
> have danced around this code in the past.
>
> (added Pavel & Rafael to Cc:).

I can't  see anything wrong with this one, but I'm not smp expert...
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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