linux-kernel - Re: [PATCH] Add Intel Ivy bridge CPU flags

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Message-ID: <20130124111340.GB13471@pd.tnic>
Date:	Thu, 24 Jan 2013 12:13:40 +0100
From:	Borislav Petkov <bp@...e.de>
To:	Michal Marek <mmarek@...e.cz>
Cc:	Alec Bickerton <alec@...angrymob.co.uk>,
	linux-kbuild@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Add Intel Ivy bridge CPU flags

On Thu, Jan 24, 2013 at 11:53:43AM +0100, Michal Marek wrote:
> On Wed, Jan 23, 2013 at 06:43:17PM +0100, Alec Bickerton wrote:
> > Hi,
> > 
> > I'd like to submit the attached patch to add Ivy Bridge processor support to the
> > processor type menu in menuconfig. Setting this configures the appropriate
> > CFLAGS (core-avx-i) for ivy bridge.
> > 
> > As this is my first kbuild patch, could somebody review it and let me know what
> > I've done wrong. ;-)
> 
> You sent it to linux-kbuild instead of x86@...nel.org. The kbuild
> maintainer is not really knowledgeable about gcc optimisation options ;).
> Nevertheless, some random comments are below. Note that I am not
> saying if the config option is useful or not.

Normally, such optimizations have a little effect on the kernel because
it doesn't normally use fpu stuff and the rest of the instructions
we need, we add ourselves (see arch/x86/include/asm/archrandom.h for
RDRAND, for example).

So, first we'd need persuasive benchmark numbers which show that a
kernel built with core-avx-i is faster at some representative workload
than mtune=generic one...

Thanks.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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