linux-kernel - Re: [PATCH 0/5] Reduce cross CPU IPI interference

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Date:	Mon, 26 Sep 2011 10:46:14 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Gilad Ben-Yossef <gilad@...yossef.com>
Cc:	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Chris Metcalf <cmetcalf@...era.com>, linux-mm@...ck.org,
	Christoph Lameter <cl@...ux-foundation.org>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>
Subject: Re: [PATCH 0/5] Reduce cross CPU IPI interference

On Mon, 2011-09-26 at 11:43 +0300, Gilad Ben-Yossef wrote:
> On Mon, Sep 26, 2011 at 10:20 AM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > On Sun, 2011-09-25 at 11:54 +0300, Gilad Ben-Yossef wrote:
> >> This first version creates an on_each_cpu_mask infrastructure API
> >
> > But we already have the existing smp_call_function_many() doing that.
> 
> I might be wrong but my understanding is that smp_call_function_many()
> does not invoke the IPI handler on the current processor. The original
> code I replaced uses on_each_cpu() which does, so I figured a wrapper
> was in order and then I discovered the same wrapper in arch specific
> code.
> 
> > The on_each_cpu() thing is mostly a hysterical relic and could be
> > completely depricated
> 
> Wont this require each caller to call smp_call_function_* and then
> check to see if it needs to also invoke the IPI handler locally ? I
> thought that was the reason for on_each_cpu existence... What have I
> missed?

Gah, you're right.. early.. tea.. more. 

Looks fine then.
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