linux-kernel - Re: Efficient x86 and x86

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Message-ID: <48A32BCF.40300@qumranet.com>
Date:	Wed, 13 Aug 2008 21:45:35 +0300
From:	Avi Kivity <avi@...ranet.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Steven Rostedt <rostedt@...dmis.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Roland McGrath <roland@...hat.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Gregory Haskins <ghaskins@...ell.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	Clark Williams <williams@...hat.com>
Subject: Re: Efficient x86 and x86_64 NOP microbenchmarks

Andi Kleen wrote:
> So for me the best strategy would be to get rid of the frame pointer
> and ignore the nops. This unfortunately would require going away
> from -pg and instead post process gcc output to insert "call mcount"
> manually. But the nice advantage of that is that you could actually 
> set up a custom table of callers built in a ELF section and with
> that you don't actually need the runtime patching (which is only
> done currently because there's no global table of mcount calls),
> but could do everything in stop_machine(). Without
> runtime patching you also don't need single part nops. 
>
> I think that would be the best option. I especially like it because
> it would prevent forcing frame pointer which seems to be costlier
> than any kinds of nosp.
>
>   

How would you deal with inlines?  Using debug information?

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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