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

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Date:	Wed, 23 Apr 2008 13:21:24 +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, Jens Axboe wrote:
> 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.

I added an smp_call_function_sync() for this purpose and kept the s390
conversion, I would very much appreciate if you could look it over. I
wont post the full patchset again today, but you can inspect it here:

http://git.kernel.dk/?p=linux-2.6-block.git;a=shortlog;h=refs/heads/generic-ipi

The interesting bits are patch #1 for the generic bits and patch #11 for
the s390 part. Thanks!

-- 
Jens Axboe

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