[Beowulf] Benchmark between Dell Poweredge 1950 And 1435

[Joshua Baker-LePain]

On Thu, 8 Mar 2007 at 11:33am, Peter St. John wrote

> Those benchmarks are quite interesting and I wonder if I interpret them at
> all correctly.
> It would seem that the Intel outperforms it's advantage in clockspeed (1/6th
> faster, but ballpark 1/3 better performance?) so the question would be
> performance gain per dollar cost (which is fine); however, for that heart
> simulation towards the end, it looks like the AMD scales up with increasing
> nodecount enormously better, and with several nodes actually outperforms the
> faster Intel.
> Should I guess at relatively poor performance of the networking on the
> motherboard used with the intel chip or does that have anything to do with
> the CPU itself?

Each benchmark was run on a single sytem with 4 CPUs (or, rather, 4 cores 
in 2 sockets) -- there was no network involved.  The difference (IMO) lies 
in the memory subsystems of the 2 architectures.

Opterons have 1 memory controller per socket (on the CPU, shared by the 2 
cores) attached to a dedicated bank of memory via a Hypertransport link 
(referred to from here on as HT).  That socket is connected to the other 
CPU socket (and its HT connected memory bank) by HT.

Xeons (still) have a single memory controller hub to which the CPUs 
communicate via the front side bus (FSB).  That single hub has 2 channels 
to memory.

So, yes, clock-for-clock (and for my usage) Xeon 51xxs are faster than 
Opterons.  But, if your code hits memory *really hard* (which that heart 
model does), then the multiple paths to memory available to the Opterons 
allow them to scale better.

This situation has existed for a long time on the Intel side.  For P4 
based Xeons it was crippling.  The new Core based Xeons, however, don't 
suffer nearly as badly (due to their big cache, maybe?).  E.g. the thermal 
simulations in that same file are pretty memory intensive themselves, and 
P4 based Xeons scaled *horribly* on them.  But the 51xx Xeons still scale 
very well on them (which surprised me).

-- 
Joshua Baker-LePain
Department of Biomedical Engineering
Duke University