linux-kernel - Re: subtle side effect of commit a1c48bb160f836

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Message-ID: <5582742D.9090206@synopsys.com>
Date:	Thu, 18 Jun 2015 13:03:01 +0530
From:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
CC:	Michal Marek <mmarek@...e.cz>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: subtle side effect of commit a1c48bb160f836

On Thursday 18 June 2015 12:40 PM, Geert Uytterhoeven wrote:
> On Thu, Jun 18, 2015 at 8:47 AM, Vineet Gupta
> <Vineet.Gupta1@...opsys.com> wrote:
>> > commit a1c48bb160f8368 "Makefile: Fix unrecognized cross-compiler command line
>> > options" moved ARCH specific cc option handling before common -Os/O2 setup.
>> >
>> > For ARC this had a subtle effect that we can no longer over-ride generic -O2 with
>> > -O3, hence a performance regression observed going from 3.13 to 3.18 (the above
>> > commit went into 3.16)
>> >
>> > I want to understand how to properly fix this. Moving the include of arch makefile
>> > will bring back the old issue. I can introduce another option to set default optim
>> > level, but only arc/m32r care about it anyways.
> Can we include $(srctree)/arch/$(SRCARCH)/Makefile twice?

Something like this would be ideal, but does that not bring back your warnings ?

> 
> Or perhaps we can not apply the extra -O* if there's already a -O* option?

Could be, but I'm not sure how to do that ?


> Alternatively, as we already have CONFIG_CC_OPTIMIZE_FOR_SIZE,
> a(nother) Kconfig option may make sense.

I can cook this one - but is it really worth doing when only 2 arches care.

Michal, do you have any opinion on how to solve this ?

-Vineet
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