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In article <38230@ut-emx.uucp> ddt@ccwf.cc.utexas.edu (David Taylor) writes:
>In article <161512.23931@timbuk.cray.com> ds@juniper09.cray.com (David Sielaff) writes:
>>In article <1990Oct9.192119.4453@murdoch.acc.Virginia.EDU> clc5q@shamash.cs.Virginia.EDU (Clark L. Coleman) writes:
>
>>>I realize that Dhrystones are not meaningful for supercomputer applications,
>>>but I thought that the scalar integer MIPS of a Cray would still exceed a
>>>PC.
Dhrystone is not geenrally meaningful these days, period.
It is well-known that compiler hacks exist (around the strcpy call),
that can boost apparent performance 30-40%, without affecting real programs
in any noticable fashion.  IT almost always overstates performance relative
to a VAX, which is why it is so popular among some computer companies :-)
...
>Understatement of the year.  SPEC is the closest that comes to the
>"whole truth", and even it is pretty far from the mark (bad pun).
SPEC as it sits, is hardly close to "the whole truth", and of course
didn't intend to be.  I'd be very suspicious of anything that claimed to
be the whole truth, as opposed to a better approximation to reality.
For supercomputers, Perfect Club probably tells you more.
-- 
-john mashey	DISCLAIMER: <generic disclaimer, I speak for me only, etc>
UUCP: 	 mash@mips.com OR {ames,decwrl,prls,pyramid}!mips!mash 
DDD:  	408-524-7015, 524-8253 or (main number) 408-720-1700
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In article <42097@mips.mips.COM> mash@mips.COM (John Mashey) writes:
>In article <38230@ut-emx.uucp> ddt@ccwf.cc.utexas.edu (David Taylor) writes:
>>In article <161512.23931@timbuk.cray.com> ds@juniper09.cray.com (David Sielaff) writes:
>>>In article <1990Oct9.192119.4453@murdoch.acc.Virginia.EDU> clc5q@shamash.cs.Virginia.EDU (Clark L. Coleman) writes:
>>
>>>>I realize that Dhrystones are not meaningful for supercomputer applications,
>>>>but I thought that the scalar integer MIPS of a Cray would still exceed a
>>>>PC.
>Dhrystone is not geenrally meaningful these days, period.
>It is well-known that compiler hacks exist (around the strcpy call),
>that can boost apparent performance 30-40%, without affecting real programs
>in any noticable fashion.  IT almost always overstates performance relative
>to a VAX, which is why it is so popular among some computer companies :-)
>...

While it is indeed true that a high Dhrystone value doesn't mean much
at all, it is certainly the case that a system giving a LOW value
has some kind of weakness. Like one of our better-known Crayettes.....

Alan P. Batson                     Academic Computing Center
apb@virginia.edu                   University of Virginia
(804) 924-0610                     Gilmer Hall
                                   Charlottesville, VA 22903

In article <42097@mips.mips.COM> mash@mips.COM (John Mashey) writes:
>SPEC as it sits, is hardly close to "the whole truth", and of course
>didn't intend to be.  I'd be very suspicious of anything that claimed to
>be the whole truth, as opposed to a better approximation to reality.
>For supercomputers, Perfect Club probably tells you more.

One comment on SPEC.  It is a workstation benchmark as far as I can see.

For supercomputers, even Perfect is not. (Some of the codes in there may be).

What is the point of running a 12 second, 16 MByte problem on a supercomputer?
And Nothing, just about, scales up linearly!  So it is useless to run
a small version of a big problem.
And, it is not always the case that you increase the dimensions and run the 
program again and you have a supercomputer application!  
At some point you need new code, new algorithm, new science.
I think in some areas applications are not being developed as fast as 
hardware is!
Can it be that too many scientists are busy making back-ups of their pc's?!

Shahin.
disclaimer,etc.

>>>>> On 14 Oct 90 02:57:57 GMT, ddt@ccwf.cc.utexas.edu (David Taylor) said:

>> Clark, when you compare PC's to Cray's, you compare VW Bug's to Ferrari's.
>> Sure, Ferrari's may not get the best mileage, but there are NO substitutes.
>> You can shop for 386 clones.  There are no Cray clones.

There use to be Cray Clones.  One went bankrupt and the other is now
owned by Cray.

By the way, the guy who owns the Lamborgini Contach parked two spots
down from by Honda might disagree with you about Ferrari substitutes.

>> If you're interested in running the Dhrystone benchmark on a Cray X/MP, you're
>> wasting extremely valuable clock cycles.  There ought to be a law against that.
>> Try comparing the Perfect Club benchmarks on a PC to a Cray.  I think you'll
>> find the Cray orders of magnitude faster.  Pay no heed to these canabis-smoking
>> "PC's-the-speed-of-Cray's" marketers.  Pipe dreamers, the lot of 'em.

Silly man. (;-) I can do anything I want with what I own, even if that
means running integer codes on a floating point machine.  A law
against that is a law against property ownereship.

But on a more serious front:  Certain workstations achieve floating
point performance within 10% of a Cray on real applications.  If you
have to split your Cray 10 ways, the workstation is a win.

>Plus the fact that the /4 part of the machine
>type means that the machine has four CPU's, which is meaningless for this
>benchmark.  All of the timings are for one processor.
>>   [... stuff ...]
>And finally, Cray's are designed
>for floating point, not integer arithmetic, so a lot of extra conversions
>from integer format to floating point format (and back) will need to be
>done.

Most user codes only run on one processor, by the way.

>> Amen!  Would you go muddin' (Texas term meaning driving pointlessly for hours
>> in a muddy field) in a Ferrari, or would you use it as a high society status
>> symbol/recreational racing vehicle?

>If you've stayed with me for this long, what it comes down to is this:
>benchmarks, like statistics, say exactly what you want them to.  They are
>not lying.  They're just not telling the whole truth.

>> Understatement of the year.  SPEC is the closest that comes to the
>> "whole truth", and even it is pretty far from the mark (bad pun).

>Dave Sielaff
>Cray Research, Inc.

>> Listen to this man.  He may not be marketing (virtue or vice?), but he is
>> enlightened.. ;)

>> 	=-ddt->

There are many paths to enlightenment.
--
Martin Fouts

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  -  Frank Zappa

In article <97@garth.UUCP> fouts@bozeman.bozeman.ingr.UUCP (Martin Fouts) writes:
> [...stuff...]
>But on a more serious front:  Certain workstations achieve floating
>point performance within 10% of a Cray on real applications.  If you
>have to split your Cray 10 ways, the workstation is a win.

One of the main thrusts of my original posts was to try to expain reasons
not to say "as compared to a Cray", etc.  That's like saying "My laptop
is faster than an IBM!"  Which IBM?  How many years old?  Doing What?
I'm not trying to deny that you have certain benchmark results, but
throwing around comments like "as compared to a Cray" is just a short
distance this side of meaningless.  I also don't believe that a Cray
is the appropriate tool for all applications.  Cray machines have been
designed with certain ideas mind, like fast processor speed, fast vector
processing, large fast memory (both main & secondary), etc.  If you need
a machine like that, perhaps a Cray (Y-MP, so I don't get flamed for
not specifying ;-) ) is what you should use.  

>>Plus the fact that the /4 part of the machine
>>type means that the machine has four CPU's, which is meaningless for this
>>benchmark.  All of the timings are for one processor.
>>>   [... stuff ...]
>>And finally, Cray's are designed
>>for floating point, not integer arithmetic, so a lot of extra conversions
>>from integer format to floating point format (and back) will need to be
>>done.
>
>Most user codes only run on one processor, by the way.

True, but my point was that if you are going to specify that your benchmark
is against a four processor machine, either run it using all four processors,
or specify that it was run on one processor.

>>> Listen to this man.  He may not be marketing (virtue or vice?), but he is
>>> enlightened.. ;)
>
>>> 	=-ddt->
>
>There are many paths to enlightenment.
>--
>Martin Fouts
>

Dave Sielaff