[gmx-users] dual-core performance
lindahl at sbc.su.se
Wed May 4 17:04:50 CEST 2005
On May 3, 2005, at 8:49 AM, David van der Spoel wrote:
> On Mon, 2005-05-02 at 23:43 -0600, Justin MacCallum wrote:
>> the new dual core Opterons have been mentioned several times on the
>> mailing list recently. We're currently investigating our options
>> for a
>> cluster upgrade later this year. Has anyone benchmarked GROMACS on
>> these machines yet? I believe both cores share a single memory
>> controller on these chips. How does/would that affect performance?
> Actually Erik Lindahl mentioned the opposite, that each processor does
> have its own memory controller. Anyway, as soon as I get the
> machines I
> will do benchmarks. We already have normal Quad Opteron machines for
> which there are benchmarks on the website. It won't differ too much,
> since GROMACS is not very memory sensitive anyway.
Sorry, I probably confused David - here's the situation as I
There are significant differences between AMD and Intel dual-core
chips. Each Athlon _die_ (i.e. physical assembly) has it's own memory
controller, which is shared by the two cores.
However, the Opterons have the entire north bridge including a system
request interface and crossbar switch built-in on the die, which
means inter-core communication is potentially very fast.
In contrast, Intel dual core chips use an external memory controller,
which will be shared by all four cores in the case of dual-dual-core
systems. To make things worse, any communication between the two
cores on a common die has to go over the external, shared, bus.
My hunch is that the dual-core Opterons should do rather well, but
not the Intel ones.
It's not realistic to expect 100% improvement, though, but as soon as
I get access to a system I'll see what we can do to tune it.
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