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From: George Bosilca (bosilca_at_[hidden])
Date: 2005-11-29 15:25:36


Tim,

It looks a little bit better. Here are the latencies for 1 to 4 bytes
messages as well as for the maximum length in Netpipe (8 MB).

old ob1:
   0: 1 bytes 694 times --> 0.06 Mbps in 137.54 usec
   1: 2 bytes 727 times --> 0.11 Mbps in 140.54 usec
   2: 3 bytes 711 times --> 0.16 Mbps in 141.54 usec
   3: 4 bytes 470 times --> 0.22 Mbps in 140.55 usec
121: 8388605 bytes 3 times --> 889.75 Mbps in 71929.97 usec
122: 8388608 bytes 3 times --> 889.72 Mbps in 71932.47 usec
123: 8388611 bytes 3 times --> 889.59 Mbps in 71943.16 usec

new ob1:
   0: 1 bytes 760 times --> 0.07 Mbps in 116.08 usec
   1: 2 bytes 861 times --> 0.13 Mbps in 116.73 usec
   2: 3 bytes 856 times --> 0.20 Mbps in 116.69 usec
   3: 4 bytes 571 times --> 0.26 Mbps in 117.48 usec
121: 8388605 bytes 3 times --> 890.37 Mbps in 71880.14 usec
122: 8388608 bytes 3 times --> 890.33 Mbps in 71883.64 usec
123: 8388611 bytes 3 times --> 890.40 Mbps in 71878.00 usec

teg:
   0: 1 bytes 867 times --> 0.07 Mbps in 114.91 usec
   1: 2 bytes 870 times --> 0.13 Mbps in 115.99 usec
   2: 3 bytes 862 times --> 0.20 Mbps in 114.37 usec
   3: 4 bytes 582 times --> 0.26 Mbps in 115.20 usec
121: 8388605 bytes 3 times --> 893.42 Mbps in 71634.49 usec
122: 8388608 bytes 3 times --> 893.22 Mbps in 71651.18 usec
123: 8388611 bytes 3 times --> 893.24 Mbps in 71649.35 usec

uniq:
   0: 1 bytes 870 times --> 0.07 Mbps in 114.59 usec
   1: 2 bytes 872 times --> 0.13 Mbps in 114.20 usec
   2: 3 bytes 875 times --> 0.20 Mbps in 114.52 usec
   3: 4 bytes 582 times --> 0.27 Mbps in 113.70 usec
121: 8388605 bytes 3 times --> 893.41 Mbps in 71635.64 usec
122: 8388608 bytes 3 times --> 893.57 Mbps in 71623.01 usec
123: 8388611 bytes 3 times --> 893.39 Mbps in 71637.67 usec

raw tcp:
   0: 1 bytes 1081 times --> 0.08 Mbps in 90.74 usec
   1: 2 bytes 1102 times --> 0.17 Mbps in 90.88 usec
   2: 3 bytes 1100 times --> 0.25 Mbps in 90.66 usec
   3: 4 bytes 735 times --> 0.34 Mbps in 89.21 usec
121: 8388605 bytes 3 times --> 894.90 Mbps in 71516.32 usec
122: 8388608 bytes 3 times --> 894.99 Mbps in 71508.84 usec
123: 8388611 bytes 3 times --> 894.96 Mbps in 71511.51 usec

The changes seems to remove around 20 micro-seconds ... that's not
bad. However, we are still 25 microseconds away from the raw TCP
stream. And these 25 microsecond should come from somewhere on the
TCP BTL because the request management is quite quick in Open MPI. I
think I have an explanation. In the Netpipe TCP they are not using
any select or poll functions, they just wait on the receive until
they get the full messages. As we do a select/poll before going to
read from the socket that should explain at least partially the
difference. But there is still a small problem. Why ob1 is 3 micro-
seconds slower than teg or uniq ?

   Thanks,
     george.

PS: I will print again the graph and send them around this evening
because the rest on the data are on my laptop (and it's at home right
now).

On Nov 29, 2005, at 12:36 PM, Tim S. Woodall wrote:

> George,
>
> Can you try out the changes I just commited on the trunk? We were
> doing
> more select/recvs then necessary.
>
> Thanks,
> Tim
>
>
> George Bosilca wrote:
>> I run Netpipe on 4 different clusters with differents OSes and
>> Eternet
>> devices. The results is that nearly the same behaviour happens all
>> the
>> time for small messages. Basically, our latency is really bad.
>> Attached
>> are 2 of the graphs on one MAC OS X cluster (wotan) and a Linux
>> 2.6.10
>> 32 bits one. The graph are for Netpipe compiled over tcp, and for
>> Open
>> MPI with all the PMLs (uniq, teg and ob1).Here is the global trend:
>>
>> - we are always slower than native TCP (what a guess!)
>>
>> - uniq is faster than teg by a fraction of second (it's more
>> visible on
>> fast networks).
>>
>> - teg and uniq are always better than ob1 in terms of latency.
>>
>> - the behaviour of ob1 differ on wotan and boba. On boba the
>> performances are a lot closer to the other PML when on wotan it's
>> like
>> 40 micro-second slower (it nearly double the raw TCP latency).
>>
>> On the same nodes I run other Netpipe with SM and MX and the
>> results are
>> pretty good. So I think we have this latency problem only on TCP.
>> I will
>> take a look to see how exactly is happens but any help is welcome.
>>
>> george.
>>
>> "We must accept finite disappointment, but we must never lose
>> infinite
>> hope."
>> Martin Luther King
>>
>>
>> ---------------------------------------------------------------------
>> ---
>>
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