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Dear Prof. McCalpin,

I am a little puzzled by the results of your "bandwidth" benchmark, and I

wonder if you could explain them to me. In a nutshell, I don't see how

you get the memory bandwidth figures from the results of running your

program.

I have some money to invest in a machine to do serious numerical

calculations which are pretty memory -intensive and so I am keenly

interested in the results. I would also be very interested in your

opinions of the various competitors. I am looking at IBM/HP/DECAlpha

/SGI Challenge machines.

You may be interested in my benchmarking results for these and other

machines. The program is a MD simulation code written by me in C.

The comparison of the "small", ie in-cache runs with the "big" 30MB

ones is *very* revealing and does sort out the sheep from the goats.

If so, just get the file "/pub/benchmark.tex" by anonymous ftp from

earth.ox.ac.uk (or eeyore.earth.ox.ac.uk or 163.1.22.1 -- we changed

our DNS records recently and it may not have propagated yet).

In any case I have some results from running your benchmark for

DEX Alpha/HP 755/735 and STardent Titan P3. My titan results differ

substantially from those you have reported -- I don't know why.

But my results agree well with the theoretical bus bandwidth

of 256 MB/sec.

sincerely

Keith Refson

--------------------------------------------------

Here are the results.

HP 755/735

feynman 22: ./a.out

--------------------------------------

Double precision appears to have 16 digits of accuracy

Assuming 8 bytes per DOUBLEPRECISION word

--------------------------------------

Timing calibration ; time = 21.00000046193599 hundredths of a second

Increase the size of the arrays if this is <30

and your clock precision is =<1/100 second

---------------------------------------------------

Function Rate (MB/s) RMS time Min time Max time

Assignment: 68.5715 .0700 .0700 .0700

Scaling : 68.5715 .0700 .0700 .0700

Summing : 72.0001 .1021 .1000 .1100

SAXPYing : 80.0001 .0971 .0900 .1000

DEC 3000/500 (150MHz AXP Alpha)

axpbb% ./a.out

--------------------------------------

Double precision appears to have 16 digits of accuracy

Assuming 8 bytes per DOUBLEPRECISION word

--------------------------------------

Timing calibration ; time = 16.49440079927444 hundredths of a second

Increase the size of the arrays if this is <30

and your clock precision is =<1/100 second

---------------------------------------------------

Function Rate (MB/s) RMS time Min time Max time

Assignment: 100.3680 0.0485 0.0478 0.0488

Scaling : 96.4323 0.0499 0.0498 0.0508

Summing : 98.3607 0.0736 0.0732 0.0742

SAXPYing : 99.6900 0.0730 0.0722 0.0732

Kubota (ex Stardent Titan P3 ) 1processor

zebedee% a.out

--------------------------------------

Double precision appears to have 16 digits of accuracy

Assuming 8 bytes per DOUBLEPRECISION word

--------------------------------------

Timing calibration ; time = 37.00000196695328 hundredths of a second

Increase the size of the arrays if this is <30 and your clock precision is =<1/100 second

---------------------------------------------------

Function Rate (MB/s) RMS time Min time Max time

Assignment: 240.0002 0.0265 0.0200 0.0300

Scaling : 240.0002 0.0283 0.0200 0.0300

Summing : 239.9993 0.0391 0.0300 0.0400

SAXPYing : 144.0001 0.0522 0.0500 0.0600

Kubota (ex Stardent Titan P3 ) 4 processors

zebedee% a.out

--------------------------------------

Double precision appears to have 16 digits of accuracy

Assuming 8 bytes per DOUBLEPRECISION word

--------------------------------------

Timing calibration ; time = 79.99998927116394 hundredths of a second

Increase the size of the arrays if this is <30 and your clock precision is =<1/100 second

---------------------------------------------------

Function Rate (MB/s) RMS time Min time Max time

Assignment: 480.0005 0.0228 0.0100 0.0300

Scaling : 240.0002 0.0349 0.0200 0.0900

Summing : 240.0002 0.0363 0.0300 0.0400

SAXPYing : 240.0002 0.0449 0.0300 0.0600

**Next message:**John R. Mashey: "Re: CPU Speed vs. Memory Bandwidth"**Previous message:**alan@msc.edu: "Re: New Chips & Memory Bandwidth"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]

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