Cluster Monitoring software?

Sadiqs sadiqs at brain.net.pk
Wed Nov 8 11:46:05 EST 2000


thank you sir. you're a regular life saver. think you should be knighted or
something. Sir Robert G. Brown..........
:)

-----Original Message-----
From: Robert G. Brown <rgb at phy.duke.edu>
To: Sadiqs <sadiqs at brain.net.pk>
Cc: Jeff Davis (Work) <jdavis at hess.com>; Beowulf Mailing List
<beowulf at beowulf.org>
Date: Monday, November 06, 2000 10:56 PM
Subject: Re: Cluster Monitoring software?


>On Mon, 6 Nov 2000, Sadiqs wrote:
>
>> i need some help with flops please.
>> how do you go around calculating flops? :)))))
>>
>>
>
>Well, you can easily see how I calculate ONE measure of >>bogus<< FLOPS
>in the open source code of cpu-rate, available on the website of:
>
>  <a href="http://www.phy.duke.edu/brahma">Brahma</a>
>
>It is something like (with lots of detail left out):
>
> double *d;             /* To test "double" floats */
> d = (double *) malloc((size_t) (size*sizeof(double)));
> total_time = 0.0;
> total_time2 = 0.0;
> for(k=1;k<=samples;k++){
>     start = gettod();
>     for(i=0;i<size;i++){
>       d[i] = 1.0;
>     }
>     for(i=0;i<size;i++){
>       d[i] = (1.0 + d[i])*(1.5 - d[i])/d[i];
>     }
>     delta = gettod() - start;
>     total_time += delta;
>     total_time2 += delta*delta;
> }
>
>(and then subtract the empty loop time and convert the times into rates,
>with a suitable definition for gettod()).  Each d[i] = (1.0 + d[i])*(1.5
>- d[i])/d[i]; is counted as four floating point operations, one each of
>add, subtract, multiply and divide.  The addressing arithmetic in the
>d-vector itself is more or less ignored, as there is always some
>addressing overhead in a loop and so it is is "part" of the cost of a
>flop, sort of, as far as I'm concerned.  This particular combination is
>chosen (with d[i] initialized to 1.0) so that it is numerically stable
>over lots of samples and yet not knowable to the compiler (so that the
>final divide is actually done and not represented as an inversion and
>multiply, which is generally a bit faster).
>
>However, note well that the rate this returns is BOGUS.  These are
>BOGOMFLOPS, just like the "mips" your kernel talks about at boot time
>are "bogomips".  This is very important to realize.  It is certainly
>entertaining and possibly useful to know how fast your computer can do
>arithmetic under certain "ideal" conditions, but >>for this code<< that
>rate can vary by a factor of >>six<< as a function of vector length.
>
>To understand this, I urge that you read the <a
>href="http://www.phy.duke.edu/brahma/cpu_summary.html">CPU Vector
>Performance Summary</a> on the Brahma website.  In it, I present a
>comparison of five reasonably current systems -- a (dual) 933 MHz PIII
>with RDRAM, two Athlons (original and Thunderbird) with PC133, a Compaq
>667 MHz XP1000, and a (dual) 466 MHz Celeron with PC66.  The figure at
>the top of this page is the measured double precision bogomflop rating
>of these CPUs executing the general code above for vector lengths (in
>bytes) ranging from 8 to 16 mega.  To quote the conclusion of this very
>short summary paper:
>
>  If nothing else, it [the figure above in the summary -- rgb] will
>  provide a fairly objective answer to the universally asked question:
>  "How fast is my CPU?" Pick a number, any number, between the maximum
>  in L1 and minimum running out of main memory (which spans almost an
>  order of magnitude in speeds!).  That's roughly how meaningful a
>  single cited speed rating for a CPU is.
>
>...not that this number cannot be used constructively, either in research
>proposals or in program or beowulf design.  Still, the >>figure itself<<
>is far >>more<< useful, as it lets one see the tremendous variation in
>effective CPU floating point performance for a certain class of core
>loop code.
>
>Hope this helps.
>
>   rgb
>
>--
>Robert G. Brown                        http://www.phy.duke.edu/~rgb/
>Duke University Dept. of Physics, Box 90305
>Durham, N.C. 27708-0305
>Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at phy.duke.edu
>
>
>


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