linux-kernel - Re: [patch] Let smp_call_function

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Date:	Tue, 15 May 2007 01:24:40 +0200
From:	Andi Kleen <ak@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	randy.dunlap@...cle.com, paulus@...ba.org,
	benh@...nel.crashing.org, David Miller <davem@...emloft.net>
Subject: Re: [patch] Let smp_call_function_single return -EBUSY.

On Monday 14 May 2007 21:11, Andrew Morton wrote:
> On Mon, 14 May 2007 11:23:17 +0200
>
> Heiko Carstens <heiko.carstens@...ibm.com> wrote:
> > From: Heiko Carstens <heiko.carstens@...ibm.com>
> >
> > All architectures that have an implementation of smp_call_function_single
> > let it return -EBUSY if it is asked to execute func on the current cpu.
> > Therefore the UP version must always return -EBUSY.
>
> smp_call_function_single() is a mess.
>
> - it's unclear to me why smp_call_function_single(cpu, ...) doesn't just
>   call the darn function if cpu==smp_processor_id().

I always wondered that too.

Also I think we really need a cpu notifier that does smp_call_single 
automatically; i  find myself reimplementing that multiple times.

> - it's unclear to me why smp_call_function_single(cpu, ...) doesn't just
>   call the darn function if CONFIG_SMP=n.

Yes.

>
> - it's unclear to me why smp_call_function_single(cpu, ...) isn't called
>   smp_call_function_on(cpu, ...)
>
> - the x86_64 version doesn't return -EBUSY: it returns zero.  Despite its
>   claim "Retrurns 0 on success, else a negative status code.".

Will fix.

-Andi
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