linux-kernel - Re: [patch] measurements, numbers about CONFIG_OPTIMIZE

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Message-ID: <20090109193506.GL26290@one.firstfloor.org>
Date:	Fri, 9 Jan 2009 20:35:06 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Dirk Hohndel <hohndel@...radead.org>,
	Matthew Wilcox <matthew@....cx>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	jim owens <jowens@...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>,
	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>, jh@...e.cz
Subject: Re: [patch] measurements, numbers about CONFIG_OPTIMIZE_INLINING=y impact

> What happens when you say -fno-inline-functions-called-once? Does it 
> disable inlining for those functions IN GENERAL, or just for the LARGE 

It does disable it in general, unless they're marked inline explicitely :

The traditional gcc 2.x rules were:

I Only inline what is marked inline (but it can decide to
not inline)
II Also inline others heuristically only with 
-O3 / -finline-functions [which we don't set in the kernel]

Then at some point this additional rule was added:

- Also inline everything static that is only called once
[on the theory that this shrinks code size which is true
according to my measurements]

-fno-inline-functions-called once disables this new rule.
It's very well and clearly defined.

-Andi

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