Impact of L2 on folding?

[FeuerFrei]

I wondered what is the impact on folding results to have let's say

Celeron 5Ghz (CedarMill 512k) vs Pentium 6xx 2mb cache 5ghz too

or Sempron vs Athlon64

[muddocktor]

It varies with the wu being run. Some wu's aren't very cache sensitive and others are very cache sensitive, size-wise. The wu's of the p147x-1481-1495-1497 series are very cache size sensitive and show a giant gain in processing speed from going from 512k to 2+ MB L2 cache. I noticed quite a gain in folding speed on these wu's with larger cache processors. For instance, back when Stanford was serving out the p147x series work, I had a Winchester 3000+ A64 (512k cache) running along with a mobile Clawhammer A64 machine (1 MB cache) and even though the mobile Clawhammer was single channel and the Winnie was dual channel on the memory, the Clawhammer system consistantly was roughly 25-30% faster on those wu's. And with the p1495 series, I first had an e6300 Allendale running in my new rig and it would average around 1200-1400 ppd rate with 2 of the p1495's folding. I replaced the Allendale (2 MB shared L2) with a Conroe e6600 (4 MB shared L2) and with the same series wu's it averages around 2000 ppd running at roughly the same clock speed. And my Dothan rig (2 MB L2), presently clocked at 2750 MHz, averages over 900 ppd with these p1495's. So cache size makes a big difference on some wu's.

But on a lot of your regular Gromacs wu's, I don't think it makes much difference at all. And you have some other wu's like the Ribo's seem to also be memory timing and bandwidth sensitive too. The QMD's that disapeared several months ago were very memory bandwith sensitive and running 2 of them on a dual core or HT Intel just flooded the hell out of the memory bus and saw almost no performance gain running 2
versus just 1.

EDIT: If you are trying to decide on processor buys, if the price is fairly close on the processors, then go ahead and get the processor with the larger L2 cache. But if it's a significant difference in price, don't worry about it.