>There's previously been several posts discussing the performance penalty
>one suffers when running multiple LL tests on a multiprocessor system
>with a single shared system bus. It would be interesting to see
>whether this
>penalty could be alleviated in a reasonably cost-effective fashion through
>use of larger L2 caches.
I had the opportunity a while back to do some crude testing with various
configurations like this...
I used the NTPrime service and put it on a few different MPS systems. Each
one was a 450 MHz Pentium II Xeon server with 1MB L2 cache Xeons in them. I
had a Dell quad CPU server, an IBM quad, and Compaq quad. When running 4
instances of NTPrime on each, I just looked at what the rollingaverage value
was after a few days of the server not doing anything else but just sitting
there running NTPrime on all the CPU's.
Okay, it wasn't really scientific, and I dont' remember the numbers exactly,
but on the Compaq, the rollingaverage was around 985-995. The Dell and IBM
had lower values, around 960-970. The memory architecture on the Compaq
servers really helps out a lot when multiple CPU's are clamoring for memory
at the same time...
I wish I could have tested one of them by telling NT to only use one CPU
(disabling SMP essentially) and seeing what the baseline rollingaverage was,
so I could compare how much a single system is affected by having multiple
CPU's running NTPrime at once, but I didn't get around to that.
>I suspect for LL tests in the ~10M range, this happy medium may be as
>'small' as 1-2MB. Are PC systems with L2 caches in this size range
>available? If so, how much of a premium does one pay for the extra cache?
Xeon's come in L2 cache sizes up to 2MB, but they are prohibitively
expensive. Most Xeon servers come with CPU's with 1MB of L2.
Beyond the Intel x86 world, I'm sure there are CPU's with much larger cache
sizes...don't Alphas come with up to 4MB of L2?
And dont the K6-III and Athlon support an L3 design, using slower memory of
course, but dedicated to each CPU so eliminating bus contention? Of course,
the K6-III doesn't do SMP, but the Athlon supports it, doesn't it? Are
there any SMP motherboards out there yet for the Athlon?
Aaron
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