[Beowulf] Q: IB message rate & large core counts (per node)?

Gilad Shainer Shainer at mellanox.com
Fri Feb 19 17:36:34 EST 2010


Nice to hear from you Greg, hope all is well.

I don't forget anything, at least for now. OSU has different benchmarks
so you can measure message coalescing or real message rate. Funny to
read that Q hated coalescing when they created the first benchmark for
that ...:-) but lets not argue on that. Nowadays it seems that QLogic
promotes the message rate as non coalescing data and I almost got bought
by their marketing machine till I looked on at the data on the wire...
interesting what the bits and bytes and symbols can tell you...


 
-----Original Message-----
From: beowulf-bounces at beowulf.org [mailto:beowulf-bounces at beowulf.org]
On Behalf Of Greg Lindahl
Sent: Friday, February 19, 2010 2:06 PM
To: beowulf at beowulf.org
Subject: Re: [Beowulf] Q: IB message rate & large core counts (per
node)?

> Mellanox latest message rate numbers with ConnectX-2 more than
> doubled versus the old cards, and are for real message rate -
> separate messages on the wire. The competitor numbers are with using
> message coalescing, so it is not real separate messages on the wire,
> or not really message rate.

Gilad,

I think you forgot which side you're supposed to be supporting.

The only people I have ever seen publish message rate with coalesced
messages are DK Panda (with Mellanox cards) and Mellanox.

QLogic always hated coalesced messages, and if you look back in the
archive for this mailing list, you'll see me denouncing coalesced
messages as meanless about 1 microsecond after the first result was
published by Prof. Panda.

Looking around the Internet, I don't see any numbers ever published by
PathScale/QLogic using coalesced messages.

At the end of the day, the only reason microbenchmarks are useful is
when they help explain why one interconnect does better than another
on real applications. No customer should ever choose which adapter to
buy based on microbenchmarks.

-- greg
(formerly employed by QLogic)


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