linux-kernel - Re: [PATCH] x86: unify x86 Makefile(s)

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Date:	Sat, 29 Dec 2007 14:54:13 +0200
From:	Adrian Bunk <bunk@...nel.org>
To:	Andi Kleen <ak@...e.de>
Cc:	Sam Ravnborg <sam@...nborg.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: unify x86 Makefile(s)

On Sat, Dec 29, 2007 at 01:16:07PM +0100, Andi Kleen wrote:
> 
> If -funit-at-a-time really increases stack size too much on some compiler
> version the right fix would be to check where it does that using make checkstack
> and then add "noinline" attributes there to prevent the compiler from inlining.
> That would prevent them.
> 
> Globally disabling it is too big a hammer.
> 
> e.g. I know XFS did it in a similar way to prevent this problem.
> 
> So I would reenable it for now and if you know it causes problems on specific
> compiler versions, Adrian, you could watch make checkstack there and submit
> noinline patches as needed.

The main point is that we are _only_ talking about gcc 3.4 on i386 - for 
more recent compilers we do not disable unit-at-a-time.

First of all our user - and therefore tester - base with this compiler 
has become quite small. And checkstack alone doesn't help that much with 
finding the problems since it only lists per-function stack usage, not 
the stack usage of the complete call chain.

People who want maximum performance and/or minimum code size anyway 
won't use a more than 3 years old compiler.

If we were talking about gcc 4.2 I would agree with you, but I simply do 
not see the point in risking regressions for gcc 3.4 users when the only 
benefit would be better code with an ancient compiler.

> -Andi

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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