Re: Attainable Memory Bandwidth

From: David Wright (wright@Stardent.COM)
Date: Wed Oct 02 1991 - 17:01:55 CDT

>If these machines use the standard UNIX approach of measuring cpu time
>in 1/100's of a second, then these cases need to be run with much
>longer vectors. They look like only 3-4 clock ticks for the fastest
>cases, and this leaves a 25-33% error in the estimates.

Spoilsport. OK, I reran the tests with vectors 4x longer than the
original program. These results are very repeatable and didn't vary
by more than 1% from run-to-run. (Yes, the first run is apt to be
slower due to faulting in the pages.)

1) Vistra 800b

 Timing calibration ; time = 375.9999923408031 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: 147.6933 0.1331 0.1300 0.1400
Scaling : 147.6933 0.1341 0.1300 0.1400
Summing : 115.2000 0.2540 0.2500 0.2600
SAXPYing : 115.2000 0.2560 0.2500 0.2600

2) ST2000: no change needed. The 2000 has a relatively slow clock
rate and I'd already tried it with vectors twice as long without
seeing any difference; doubling it again still made no difference
(although the results started to vary more due to more contention for
the cpu from other sources).

>By the way, what is the clock speed on the Vistra 800b?

40 MHz. (FYI, this is also true for the V800e and V800ex, which are
different graphics, not different host architecture.)

>And is the ST2000 one of the older MIPS-based machines?

Nope. That's the P2/P3 (now known as the ST1500 and ST3000). The
ST2000 is the original Stellar architecture (proprietary). Still
being sold, (including refurbished used machines, mostly the earlier
but very similar ST1000), and the price/perf isn't bad at all.

>I have access to a P3 that I will get this stuff run on, too....

Good. I tried it myself here and got numbers in the ballpark of the
ST2000 (slightly better, maybe 15%), but since I'm an old Stellarite,
I wasn't sure I was using the compiler/system to best advantage. (I
don't even know all the details on the ST2000 -- "Dammit, Jim, I'm a
kernel programmer, not a benchmarker!")

  -- David Wright, Stardent Computer Inc

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