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

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Message-ID: <20090109181952.GI26290@one.firstfloor.org>
Date:	Fri, 9 Jan 2009 19:19:52 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	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>,
	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,
	richard.guenther@...il.com
Subject: Re: [patch] measurements, numbers about CONFIG_OPTIMIZE_INLINING=y impact

> So we do have special issues. And exactly _because_ we have special issues 
> we should also expect that some compiler defaults simply won't ever really 
> be appropriate for us.

I agree that the kernel needs quite different inlining heuristics
than let's say a template heavy C++ program. I guess that is 
also where our trouble comes from -- gcc is more tuned for the
later. Perhaps because the C++ programmers are better at working
with the gcc developers?

But it's also not inconceivable that gcc adds a -fkernel-inlining or
similar that changes the parameters if we ask nicely. I suppose
actually such a parameter would be useful for far more programs
than the kernel.

-Andi

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