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

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Date:	Fri, 9 Jan 2009 16:33:04 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Theodore Tso <tytso@....edu>
cc:	Richard Guenther <richard.guenther@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Matthew Wilcox <matthew@....cx>,
	Andi Kleen <andi@...stfloor.org>,
	Dirk Hohndel <hohndel@...radead.org>,
	"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>,
	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


On Fri, 9 Jan 2009, Theodore Tso wrote:

> I'm beginning to think that for the kernel, we should just simply
> remove CONFIG_OPTIMIZE_INLINING (so that inline means
> "always_inline"), and -fno-inline-functions
> -fno-inline-functions-called-one (so that gcc never inlines functions
> behind our back) --- and then we create tools that count how many times functions get used, and how big functions are, so that we can flag if some 
> function really should be marked inline when it isn't or vice versa.   
> 
> But given that this is a very hard thing for an automated program
> todo, let's write some tools so we can easily put a human in the loop,
> who can add or remove inline keywords where it makes sense, and let's
> give up on gcc being able to "guess" correctly.
> 
> For some things, like register allocation, I can accept that the
> compiler will usually get these things right.  But whether or not to
> inline a function seems to be one of those things that humans (perhaps
> with some tools assist) can still do a better job than compilers.

Adding a function histogram in ftrace should be trivial. I can write one 
up if you want. It will only count the functions not inlined.

-- Steve
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