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

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Message-ID: <alpine.LFD.2.00.0901111248060.6528@localhost.localdomain>
Date:	Sun, 11 Jan 2009 12:51:31 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
cc:	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, 11 Jan 2009, Andi Kleen wrote:
> 
> Was -- i think that got fixed in gcc. But again only in newer versions.

I doubt it. People have said that about a million times, it has never 
gotten fixed, and I've never seen any actual proof.

I think that what got fixed was that gcc now at least re-uses stack slots 
for temporary spills. But only for things that fit in registers - not if 
you actually had variables that are big enough to be of type MEM. And the 
latter is what tends to eat stack-space (ie structures etc on stack).

But hey, maybe it really did get fixed. But the last big stack user wasn't 
that long ago, and I saw it and I have a pretty recent gcc (gcc-4.3.2 
right now, it could obviously have been slightly older back a few months 
ago).

		Linus
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