linux-kernel - Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning

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Message-ID: <20090112015620.GA6428@shareable.org>
Date:	Mon, 12 Jan 2009 01:56:20 +0000
From:	Jamie Lokier <jamie@...reable.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Harvey Harrison <harvey.harrison@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	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>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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>,
	Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning

Ingo Molnar wrote:
> If it's used once in a single .c file it should be inlined even if
> it's large.

As Linus has pointed out, because of GCC not sharing stack among
different inlined functions, the above is surprisingly not true.

In kernel it's a problem due to raw stack usage.

In userspace apps (where stack used is larger), inlining single-call
functions could, paradoxically, run slower due to increased stack
dcache pressure for some larger functions.

-- Jamie
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