Date: Fri, 9 Jan 2009 16:33:04 -0500 (EST)
From: Steven Rostedt <rostedt@goodmis.org>
To: Theodore Tso <tytso@mit.edu>
cc: Richard Guenther <richard.guenther@gmail.com>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Matthew Wilcox <matthew@wil.cx>, Andi Kleen <andi@firstfloor.org>,
       Dirk Hohndel <hohndel@infradead.org>, "H. Peter Anvin" <hpa@zytor.com>,
       Ingo Molnar <mingo@elte.hu>, jim owens <jowens@hp.com>,
       Chris Mason <chris.mason@oracle.com>,
       Peter Zijlstra <peterz@infradead.org>, paulmck@linux.vnet.ibm.com,
       Gregory Haskins <ghaskins@novell.com>,
       Andrew Morton <akpm@linux-foundation.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       linux-fsdevel <linux-fsdevel@vger.kernel.org>,
       linux-btrfs <linux-btrfs@vger.kernel.org>,
       Thomas Gleixner <tglx@linutronix.de>, Nick Piggin <npiggin@suse.de>,
       Peter Morreale <pmorreale@novell.com>,
       Sven Dietrich <SDietrich@novell.com>, jh@suse.cz
Subject: Re: [patch] measurements, numbers about CONFIG_OPTIMIZE_INLINING=y
 impact
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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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