linux-kernel - Re: [PATCH 0 of 9] x86/smp function calls: convert x86 tlb flushes to use function calls [POST 2]

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Date:	Tue, 19 Aug 2008 11:31:30 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
	Andi Kleen <andi@...stfloor.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [PATCH 0 of 9] x86/smp function calls: convert x86 tlb flushes
	to use function calls [POST 2]

* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> Ingo Molnar wrote:
> > nice stuff!
> >
> > I suspect the extra cost might be worth it for two reasons: 1) we could 
> > optimize the cross-call implementation further
> 
> Unfortunately, I think the kmalloc fix for the RCU issue is going to 
> hurt quite a lot.

yeah :-(

Nick, is there any way to get rid of that kmalloc() in the async 
function call case? The whole premise of the smp_function_call() rewrite 
was that it's faster - and now it's measurably slower.

At least we could/should perhaps standardize/generalize all the 
'specific' IPI handlers into the smp_function_call() framework: if 
function address equals to a pre-cooked IPI entry point we could call 
that function without a kmalloc. As these are all hardwired, 
__builtin_is_constant_p() could come to the help as well. Hm?

	Ingo
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