[Beowulf] Re: Re: Home beowulf - NIC latencies

Greg Lindahl lindahl at pathscale.com
Thu Feb 10 21:36:20 EST 2005


On Thu, Feb 10, 2005 at 01:35:06PM -0700, Maurice Hilarius wrote:

> Further, all of these lovely benchmarks lack one really important detail:
> Comparisons between different interfaces and drivers MUST show CPU usage 
> while running them.

No. If you want to look at that, run a real application and watch the
wall time. It's extremely hard to get a good estimate of cpu usage out
of a microbenchmark, and running "top" or /bin/time to do it is
definitely bogus.

> If I have a fantastic device that uses infinitely small time (latency) 
> and moves huge amounts of data (bandwidth) but in doing so it takes 80% 
> of a CPU, we do not have a useful solution..

If large cpu usage is a problem, it will show up nicely in real
application benchmarks.

> What we all need is some form of useful standardized benchmarks that 
> looks like real world code from a number of different disciplines, that 
> we can use to test the hardware, so we may compare results in a 
> meaningful manner.

Amen. So use the MM5 t3a benchmark, maybe even SPEC HPC, the canned
benchmarks for Amber, Charmm, DL_POLY, etc. The NAS Parallel
Benchmarks are also good, they are much closer to real apps than
microbenchmarks.

-- greg
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