linux-kernel - Re: [PATCH 2/11] x86: convert to generic helpers for IPI function calls

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Date:	Wed, 23 Apr 2008 03:36:17 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Jens Axboe <jens.axboe@...cle.com>,
	linux-arch@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	peterz@...radead.org, sam@...nborg.org
Subject: Re: [PATCH 2/11] x86: convert to generic helpers for IPI function calls

On Tue, Apr 22, 2008 at 06:22:17PM -0700, Linus Torvalds wrote:
> 
> 
> On Wed, 23 Apr 2008, Nick Piggin wrote:
> > 
> > The "too expensive to check the shared queue" is one aspect of it. The
> > shared queue need not have events *for us* (at least, unless Jens has
> > changed the implementation a bit) but it can still have events that we
> > would need to check through.
> > 
> > I don't think deadlock is a problem (any more than with multiple vectors).
> 
> I'm happy with it either way, but as pointed out by Ralf, for the MIPS 
> version of the patch there aren't even other vectors available.
 
Yep.

> So sharing the vector is going to be a requirement on other architectures, 
> maybe we should look at whether we can make it generic and peform well 
> regardless?

I don't think it will perform terribly _poorly_ by sharing the vector.
If you have a look at how serialised the old code is...

If there is a noticable slowdown anywhere, we could I suppose create a
2nd variant for small numbers of CPUs, or shared vector case, but I'd
say the existing code should be fine I think.
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