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Date: Fri, 25 Aug 2006 07:23:03 -0700
From: "M. Edward (Ed) Borasky" <znmeb@cesmail.net>
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Subject: Re: [gentoo-science] Re: [Fwd: Re: [atlas-devel] 1) ATLAS shared
libraries; 2) "ASM" -> "ASM VOLATILE"]
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Markus Dittrich wrote:
> On Fri, 25 Aug 2006, Adam Pityszek wrote:
>
>>> Dear Markus, gentoo-science guys,
>>>
>>> Please find below the reply from Clint to my yesterday's email related to
>>> our work on ATLAS shared libraries in Gentoo.
>>>
>>> Markus, I think we can help with answering the questions (2) and (3). Of
>>> course, volunteers from gentoo-science are welcome as well.
>>>
>>> BR,
>>> /ediap
>>>
>>> (1) Is it true that the extra pointer may still be used if we restore
>>> it at
>>> end of assembly routine?
>>> (2) Does throwing the -fpic or other required compiler flag changes
>>> change
>>> the best cases (thus necessitating doubling the arch defaults)?
>>> (3) What is the overall performance affect when using .so?
>>>
>>> I've tried to answer (1) by looking at some docs, but never got convinced
>>> either way. I've been meaning to write a resister stress-test to see if
>>> I can make gcc use the reserved register in a function w/o global data.
>>> Perhaps you know?
>>>
>>> You guys could help with (2) & (3) if you like. You could build
>>> out-of-box
>>> to .a on whatever machines you can, and then build it to .so using your
>>> gentoo harness, and post some head-to-head timings . . . If, as we
>>> suspect,
>>> the difference is essentially zero, that makes .so a lot more
>>> attractive . . .
>>>
>
> Hi Adam,
>
> Thanks for talking to upstream about this and Clint's response
> sounds encouraging. We could definitely help out with 2) and 3);
> it would be good to know anyway how well we do with our shared libs. In
> doing so we should also test the impact of using
> the 387 floating point unit versus the sse instruction set. According to
> Clint, the former can give a significant performance
> gain on some CPU's. If that is the case it might be worth a note in the
> ebuild to make our users aware of it.
>
> We should get a hold of a nice benchmark suite for this purpose; Clint
> has posted one on this gcc bug
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27827
> which we might be able to use. I'll have a look at it.
>
> Best,
> Markus
>
>
> -- Markus Dittrich (markusle)
> Gentoo Linux Developer
> Scientific applications
If you have the time, you can turn off all of the pre-conceived notions
Atlas has about your architecture and let it benchmark itself. In fact,
for the hard-core number crunchers, you might actually want to put a USE
flag in the ebuild to do a "brute-force" assume-nothing compile, warning
them that it takes a long time and that it should be run after an
"emerge -f" with Linux in single-user mode. My recollection is that it
used to take about 8 hours on a 1.3 GHz Athlon Thunderbird.
--
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