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

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Message-ID: <20090111203441.GQ26290@one.firstfloor.org>
Date:	Sun, 11 Jan 2009 21:34:41 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Linus Torvalds <torvalds@...ux-foundation.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

> Isn't the ioctl switch stack issue a separate GCC bug?
> 
> It was/is assigning assigning separate space for local variables which

Was -- i think that got fixed in gcc. But again only in newer versions.

> are mutually exclusive. So instead of the stack footprint of the
> function with the switch() being equal to the largest individual stack
> size of all the subfunctions, it's equal to the _sum_ of the stack sizes
> of the subfunctions. Even though it'll never use them all at the same
> time.
> 
> Without that bug, it would have been harmless to inline them all.

True.

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