linux-kernel - Re: [PATCH x86] [15/16] Force __cpuinit on for CONFIG_PM without HOTPLUG

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Date:	Tue, 15 Jan 2008 19:29:04 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	Adrian Bunk <bunk@...nel.org>, rjw@...k.pl, pavel@...e.cz,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH x86] [15/16] Force __cpuinit on for CONFIG_PM without HOTPLUG_CPU

On Tue, Jan 15, 2008 at 07:21:42PM +0100, Sam Ravnborg wrote:
> With default options to gcc my .config produces ~65 warnings
> but with -fno-unit-a-time I get 112 warnings.
> Solely due to less inlining done by gcc.
> 
> So there are two sources for the 'randomization':
> a) The actual config
> b) The sometimes agressive inlining

Inlining should not be random.  And how does inlining cause such a warning?
> 
> a) will be addressed by having separate sections for each
> __init* type that is at link time combined where it belongs.

One problem I ran into the past was that older binutils seem
to have some exponential behaviour with a lot of named sections
and run very slowly.

> 
> b) is addressed by a Kernel Hacking option which
>    1) uses -fno-unit-at-a-time to get less gcc inlining
>    2) maybe make all __*init function no-inline
>    3) maybe disable inlining globally
> 
> > > And I will add a config option to:
> > > - set -fno-unit-at-a-time
> > 
> > I was told future gcc versions would remove that. Why do you
> > want it?
> Are there any better way to tell gcc no to inline so agressively?

You can either sprinkle noinlines or set specific --params to throttle
back the inliner. The later is very gcc version specific unfortunately.

-Andi
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