linux-kernel - Re: [rfc][patch] x86-64 new smp_call

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Message-ID: <20080227221407.GA26067@wotan.suse.de>
Date:	Wed, 27 Feb 2008 23:14:07 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andi Kleen <ak@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-arch@...r.kernel.org
Subject: Re: [rfc][patch] x86-64 new smp_call_function design

On Wed, Feb 27, 2008 at 04:02:10PM +0100, Ingo Molnar wrote:
> 
> * Nick Piggin <npiggin@...e.de> wrote:
> 
> > > the two structures are quite similar in size and role - why not have 
> > > a type field and handle them largely together? I think we should try 
> > > to preserve a single queue and a single vector - that would remove a 
> > > number of ugly special-cases from the patch.
> > 
> > A single queue will kill one of the big fundamental scalability 
> > improvements of the call_single. That's the problem.
> 
> hm, indeed. Then how about the other way around: couldnt the normal 
> all-cpus SMP function call be implemented transparently via using 
> smp_call_single() calls?

That's possible, but it is slower and less scalable on my 8-way, and
I suspect it might become even slower than the generic code on larger
systems.

> The vector duplication is really ugly and feels 
> wrong.

Why?
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