Hi Kevin,
I believe that your company is using this list for pure marketing wars
for a long time, so don't be surprise when someone responds back.
If you want to put technical or performance data, and than to make
conclusions out of it, be sure to compare apples to apples. It is easy
use the lower performance device results of your competitor and
than to
attack his "architecture" or his entire product line. If this is not a
marketing war, than I would be interesting to know what you call a
marketing war....
G
-----Original Message-----
From: Kevin Ball [mailto:[EMAIL PROTECTED]
Sent: Friday, July 20, 2007 11:27 AM
To: Gilad Shainer
Cc: Brian Dobbins; beowulf@beowulf.org
Subject: RE: [Beowulf] MPI2007 out - strange pop2 results?
Hi Gilad,
Thank you for the personal attack that came, apparently without even
reading the email I sent. Brian asked about why the publicly
available,
independently run MPI2007 results from HP were worse on a particular
than the Cambridge cluster MPI2007 results. I talked about three
contributing factors to that. If you have other reasons you want
to put
forward, please do so based on data, rather than engaging in a blatant
ad hominem attack.
If you want to engage in a marketing war, there are venues with
which
to do it, but I think on the Beowulf mailing list data and coherent
thought are probably more appropriate.
-Kevin
On Fri, 2007-07-20 at 10:43, Gilad Shainer wrote:
Dear Kevin,
You continue to set world records in providing misleading
information.
You had previously compared Mellanox based products on dual
single-core machines to the "InfiniPath" adapter on dual dual-core
machines and claim that with InfiniPath there are more Gflops....
This
latest release follow the same lines...
Unlike QLogic InfiniPath adapters, Mellanox provide different
InfiniBand HCA silicon and adapters. There are 4 different silicon
chips, each with different size, different power, different price and
different performance. There is the PCI-X device (InfiniHost), the
single-port device that was deigned for best price/performance
(InfiniHost III Lx), the dual-port device that was designed for best
performance (InfiniHost III Ex) and the new ConnectX device that was
designed to extend the performance capabilities of the dual port
device. Each device provide different price and performance points
(did I said different?).
The SPEC results that you are using for Mellanox, are of the single
port device. And even that device (that its list price is probably
half of your InfiniPath) had better results with 8 server nodes than
yours....
Your comparison of InfiniPath to the Mellanox single-port device
should have been on price/performance and not on performance. Now, if
you want to really compare performance to performance, why don't you
use the dual port device, or even better, ConnectX? Well... I will do
it for you.
Every time I had compared my performance adapters to yours, your
adapters did not even come close...
Gilad.
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:beowulf-
[EMAIL PROTECTED]
On Behalf Of Kevin Ball
Sent: Thursday, July 19, 2007 11:52 AM
To: Brian Dobbins
Cc: beowulf@beowulf.org
Subject: Re: [Beowulf] MPI2007 out - strange pop2 results?
Hi Brian,
The benchmark 121.pop2 is based on a code that was already
important to QLogic customers before the SPEC MPI2007 suite was
released (POP, Parallel Ocean Program), and we have done a fair
amount
of analysis trying to understand its performance characteristics.
There are three things that stand out in performance analysis on
pop2.
The first point is that it is a very demanding code on the
compiler.
There has been a fair amount of work on pop2 by the PathScale
compiler
team, and the fact that the Cambridge submission used the PathScale
compiler while the HP submission used the Intel compiler accounts for
some (the serial portion) of the advantage at small core counts,
though scalability should not be affected by this.
The second point is that pop2 is fairly demanding of IO. Another
example to look at for this is in comparing the AMD Emerald Cluster
results to the Cambridge results; the Emerald cluster is using NFS
over GigE from a single server/disk, while Cambridge has a much more
optimized IO subsystem. While on some results Emerald scales better,
for pop2 it scales only from 3.71 to 15.0 (4.04X) while Cambridge
scales from 4.29 to 21.0 (4.90X). The HP system appears to be using
NFS over DDR IB from a single server with a RAID; thus it should
fall
somewhere between Emerald and Cambridge in this regard.
The first two points account for some of the difference, but by no
means all. The final one is probably the most crucial. The code
pop2
uses a communication pattern consisting of many small/medium sized
(between 512 bytes and 4k) point to point messages punctuated by
periodic tiny (8b) allreduces. The QLogic InfiniPath architecture
performs far better in this regime than the Mellanox InfiniHost
architecture.
This is consistent with what we have seen in other application
benchmarking; even SDR Infiniband based off of the QLogic InfiniPath
architecture performs in general as well as DDR Infiniband based on
the Mellanox InfiniHost architecture, and in some cases better.
Full disclosure: I work for QLogic on the InfiniPath product line.
-Kevin
On Wed, 2007-07-18 at 18:50, Brian Dobbins wrote:
Hi guys,
Greg, thanks for the link! It will no doubt take me a little
while to parse all the MPI2007 info (even though there are only a
few submitted results at the moment!), but one of the first things I
noticed was that performance of pop2 on the HP blade system was
beyond
atrocious... any thoughts on why this is the case? I can't see any
logical reason for the scaling they have, which (being the first
thing
I noticed) makes me somewhat hesitant to put much stock into the
results at the moment. Perhaps this system is just a statistical
blip
on the radar which will fade into noise when additional results are
posted, but until that time, it'd be nice to know why the results
are the way they are.
To spell it out a bit, the reference platform is at 1 (ok, 0.994)
on
16 cores, but then the HP blade system at 16 cores is at 1.94. Not
bad there. However, moving up we have:
32 cores - 2.36
64 cores - 2.02
128 cores - 2.14
256 cores - 3.62
So not only does it hover at 2.x for a while, but then going from
128 -> 256 it gets a decent relative improvement. Weird.
On the other hand, the Cambridge system (with the same processors
and a roughly similar interconnect, it seems) has the follow scaling
from 32->256 cores:
32 cores - 4.29
64 cores - 7.37
128 cores - 11.5
256 cores - 15.4
... So, I'm mildly confused as to the first results. Granted,
different compilers are being used, and presumably there are other
differences, too, but I can't see how -any- of them could result in
the scores the HP system got. Any thoughts? Anyone from HP (or
QLogic) care to comment? I'm not terribly knowledgeable about the
MPI
2007 suite yet, unfortunately, so maybe I'm just overlooking
something.
Cheers,
- Brian
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