linux-kernel - Re: gcc inlining heuristics was Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning

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Message-ID: <20090112005228.GS26290@one.firstfloor.org>
Date:	Mon, 12 Jan 2009 01:52:28 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Harvey Harrison <harvey.harrison@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	paulmck@...ux.vnet.ibm.com, Gregory Haskins <ghaskins@...ell.com>,
	Matthew Wilcox <matthew@....cx>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-btrfs <linux-btrfs@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nick Piggin <npiggin@...e.de>,
	Peter Morreale <pmorreale@...ell.com>,
	Sven Dietrich <SDietrich@...ell.com>, jh@...e.cz
Subject: Re: gcc inlining heuristics was Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning

On Sun, Jan 11, 2009 at 04:21:03PM -0800, Linus Torvalds wrote:
> 
> 
> On Mon, 12 Jan 2009, Andi Kleen wrote:
> > 
> > so at least least for this case it works. Your case also doesn't work 
> > for me. So it looks like gcc didn't like something you did in your test 
> > program.
> 
> I very intentionally used _different_ types.
> 
> If you use the same type, gcc will apparenrly happily say "hey, I can 
> combine two variables of the same type with different liveness into the 
> same variable".

Confirmed.

> But that's not the interesting case.

Weird. I wonder where this strange restriction comes from. It indeed
makes this much less useful than it could be :/

-Andi
-- 
ak@...ux.intel.com
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