linux-kernel - Re: x86: Is there still value in having a special tlb flush IPI vector?

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Message-ID: <20080729120237.GH30344@one.firstfloor.org>
Date:	Tue, 29 Jul 2008 14:02:37 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	Jens Axboe <jens.axboe@...cle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: x86: Is there still value in having a special tlb flush IPI vector?

On Mon, Jul 28, 2008 at 11:29:18PM -0700, Jeremy Fitzhardinge wrote:
> Andi Kleen wrote:
> >>>Now that normal smp_function_call is no longer an enormous bottleneck, 
> >>>      
> >
> >Hmm? It still uses a global lock at least as of current git tree.
> 
> Yes, but it's only held briefly to put things onto the list.  It doesn't 
> get held over the whole IPI transaction as the old smp_call_function 
> did, and the tlb flush code still does.  RCU is used to manage the list 
> walk and freeing, so there's no long-held locks there either.

If it bounces regularly it will still hurt.

-Andi
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