Thanks for response, I'll try some other tests with another distros
if I have time.
Le 13 nov. 05 à 20:59, Jeff Squyres a écrit :
> With 2 nodes, LAM will use a simple scheme -- the non-root will
> send to
> the root, and the root will copy the sendbuf to the recvbuf.
>
> I don't know offhand what would cause the results shown below,
> although
> we have seen issues with the memcpy's in some OS's/Linux distros
> (i.e.,
> some work better than others), particularly if the data it is copying
> is page- or max-datatype-size-aligned or not (e.g., aligned on 8 byte
> boundaries).
>
>
> On Nov 11, 2005, at 2:49 PM, David Ulrich wrote:
>
>> Hi,
>>
>> I try some basic benchmark on a small cluster. It's P4 2,4GHz with
>> 83842 ethernet card (mtu 1500).
>> With 2 nodes I have this:
>> http://aspirine.li/mesure2.pdf
>>
>> on Ox it's the size of the packets in bytes, on Oy it's time in
>> seconds
>>
>> We see very well the mtu effects, but I can't explain the second
>> curve!?
>> This is what I have done:
>> - I use a float table which grow every loop
>> - I send a table 100 times to do get a good time benchmark
>>
>> This is a part of the result, where we see that every 10bytes I have
>> strange results:
>>
>> nodes;time[s];size [bytes]
>> ------------------------------
>> 2;0.000358077;16404<--
>> 2;0.000343283;16408
>> 2;0.000342555;16412
>> 2;0.000342477;16416
>> 2;0.000342885;16420
>> 2;0.000342765;16424
>> 2;0.00034233;16428
>> 2;0.00034231;16432
>> 2;0.000342906;16436
>> 2;0.000342528;16440
>> 2;0.000360112;16444<--
>> 2;0.000343095;16448
>> 2;0.000342613;16452
>> 2;0.000342823;16456
>> 2;0.000342695;16460
>> 2;0.000342781;16464
>> 2;0.000342082;16468
>> 2;0.000342706;16472
>> 2;0.000342361;16476
>> 2;0.000342908;16480
>> 2;0.000358126;16484<--
>> 2;0.000342697;16488
>> 2;0.000342495;16492
>> 2;0.000342806;16496
>> 2;0.000342006;16500
>> 2;0.000342573;16504
>> 2;0.000343114;16508
>> 2;0.000343439;16512
>> 2;0.000343044;16516
>> 2;0.000343867;16520
>> 2;0.000357508;16524<--
>>
>> If somebody could explain me?
>>
>> Regards
>>
>> Ulrich David
>> _______________________________________________
>> This list is archived at http://www.lam-mpi.org/MailArchives/lam/
>>
>
> --
> {+} Jeff Squyres
> {+} The Open MPI Project
> {+} http://www.open-mpi.org/
>
> _______________________________________________
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