linux-kernel - Re: [PATCH 11/11] s390: convert to generic helpers for IPI function calls

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Date:	Wed, 23 Apr 2008 10:11:48 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	npiggin@...e.de, torvalds@...ux-foundation.org,
	peterz@...radead.org, sam@...nborg.org,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH 11/11] s390: convert to generic helpers for IPI  function calls

On Wed, Apr 23 2008, Heiko Carstens wrote:
> On Tue, Apr 22, 2008 at 08:50:27PM +0200, Jens Axboe wrote:
> > This converts s390 to use the new helpers for smp_call_function() and
> > friends, and adds support for smp_call_function_single(). Not tested,
> > but it compiles.
> > 
> > Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
> > Cc: Heiko Carstens <heiko.carstens@...ibm.com>
> > Signed-off-by: Jens Axboe <jens.axboe@...cle.com>
> 
> Your generic patch changes semantics of smp_call_function(). At least the
> s390 version of smp_call_function() mask used to not return unless all IPIs
> where received on the target cpus.
> Your patch changes that. It will already return as soon as all IPIs have
> been sent. Unfortunately Martin's etr code in arch/s390/kernel/time.c

Yep, this is what I mentioned in the intro mail.

> relies on exactly the old semantics.

OK, I could not see anything which relied on that and I did think that
it was a somewhat odd interface. By the time that smp_call_function()
stops waiting for startups, we could easily be in the condition that the
N-1 CPUs executed the function part a long time ago. I just didn't see
much usefulness in that, you may as well just set wait == 1 in that
case.

> Since this seems to be an s390 only issue, could you just drop the s390
> conversion patch? We'll have to think about how to change the err code
> and convert later I guess.

I'll drop the s390 bits. I can easily add something like
smp_call_function_foo() that has this behaviour.

-- 
Jens Axboe

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