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Date: Mon, 4 May 2009 19:55:49 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Arjan van de Ven <arjan@infradead.org>
Cc: Tobias Doerffel <tobias.doerffel@gmail.com>,
       "H. Peter Anvin" <hpa@zytor.com>, Willy Tarreau <w@1wt.eu>,
       Thomas Gleixner <tglx@linutronix.de>,
       Suresh Siddha <suresh.b.siddha@intel.com>,
       "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: Specific support for Intel Atom architecture
Message-ID: <20090504175549.GA16720@elte.hu>
References: <200904301408.09370.tobias.doerffel@gmail.com> <20090503053821.GI570@1wt.eu> <49FD3E56.3010803@zytor.com> <200905031308.51316.tobias.doerffel@gmail.com> <20090504131457.GA25844@elte.hu> <20090504063258.00d035b2@infradead.org>
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* Arjan van de Ven <arjan@infradead.org> wrote:

> On Mon, 4 May 2009 15:14:57 +0200
> Ingo Molnar <mingo@elte.hu> wrote:
> 
> > 
> > * Tobias Doerffel <tobias.doerffel@gmail.com> wrote:
> > 
> > > Am Sonntag, 3. Mai 2009 08:48:54 schrieb H. Peter Anvin:
> > > > Willy Tarreau wrote:
> > > > >> $(call cc-option,-march=atom,-march=i686)
> > > > >
> > > > > if it's an in-order architecture, wouldn't it be better to tune
> > > > > for i386 or i486 instead ?
> > > >
> > > > Possibly.  It would be worth measuring.
> > >
> > > How would one do that (never benchmarked kernel stuff before)?
> > 
> > A standard method is to run lmbench and compare the results - 
> > lmbench has a built-in 'report comparison between two runs' 
> > feature.
> 
> well... you're normally REALLY hard pressed to measure compiler 
> differences this way.....
> 
> normally compiler options get benchmarked using speccpu and the 
> like....

Well, if there's no measurable difference in lmbench at all then the 
options probably dont matter that much. If some workload is found 
where compiler options show a difference then that matters. Speccpu 
only matters if those compiler options also help the kernel, in a 
measurable way.

	Ingo