[gmx-users] 8MB CPU cache vs 4MB CPU cache: large difference in performance?

[David van der Spoel]

Frankie Montenegro wrote:
> Hi,
> 
> I am about to purchase several units with Intel's quadcore q6600
> processors. Since about 80% of our work is done with Gromacs, I
> figured this list is a place to ask performance questions.
> 
> I was wondering if there would be any significant benefit in having a
> q6600 processor with 8MBof L2 cache over the identical processor
> with 4MB of L2 cache. The price difference is about 60$,which doesn't
> seem much,  but could pile up if we end up buying more then a few units.
> 
obviously we don't have a lot of benchmarks of these brand new 
processors. you could try to get evaluation units to test them yourself. 
a number of factors play in:
- typical system size
- how much do you want to run in parallel?
- if so, do you intend to buy a fast network as well?

larger systems have more use for cache than small systems, but if you 
run parallel you get all cache from all CPUs, which makes that we 
sometimes see superscaling: a run that gets scales better than the 
number of processors due to runs fitting in cache all of sudden. Bottom 
line is more cache is better, but whether you get more bang for the buck 
is another matter.


> Thanks for your help.
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-- 
David van der Spoel, Ph.D.
Molec. Biophys. group, Dept. of Cell & Molec. Biol., Uppsala University.
Box 596, 75124 Uppsala, Sweden. Phone:	+46184714205. Fax: +4618511755.
spoel at xray.bmc.uu.se	spoel at gromacs.org   http://folding.bmc.uu.se