[Beowulf] MVAPICH2 and osu_latency

Ashley Pittman apittman at concurrent-thinking.com
Fri Jun 13 06:02:07 EDT 2008


On Fri, 2008-06-13 at 05:11 +0200, Jan Heichler wrote:
> >
> 
> 
> So you're concerned with the gap
> between the 2.63 us that OSU
> measured and your 3.07 us you
> measured.  I wouldn't be too
> concerned.
> 
> 1st: i get a value of 2.96 with MVAPICH 1.0.0 - this is exactly the
> value that i find on the mvapich website ;-)
> 
> 
> It is not about being concerned not to get "optimal performance" - i
> know that such micro-benchmarks are of limited use... but i have a
> customer requirement. And since it seems possible it would be helpfull
> to get there

Rule #1.  Don't commit yourself to a latency/bandwidth figure unless you
have run the specific micro-benchmark *on the specific chipset/hardware
configuration* you intend to deliver this commitment on.  0.4uS is well
withing the bounds of fluctuation you get from different PCI chipsets.

You're probably best of going back to the hardware vendor to see if
there is anything they can tweak (mmtr perhaps?) but beyond that I
suspect your problem will have political solution rather than a
technical one.

> The value is everytime the same. Shouldn't it be different then every
> run? And: how can i move the process? numactl or taskset just works on
> the local process i assume. How can i move the "remote process" on the
> other host?

Run numactl on the other host as well.  That said it's unusual for the
value to the be same every run, this probably won't change anything as
all numactl can do is to stabilise the results towards the bottom of the
range observed without it.

Ashley Pittman.


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