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Old 2011-03-14, 11:13   #1
(loop (#_fork))
fivemack's Avatar
Feb 2006
Cambridge, England

13×491 Posts
Default Small(ish) matrices on fast computers

I ran an easy (C131) problem on the new dual-Xeon-5660 machine at work, with -t 3 through -t 12:

Hyperthreading enabled, though there are 12 'real' threads and I would hope I could trust Linux (Ubuntu 10.04) to use real threads before doubling up.

Number of threads : reported BLanczosTime in seconds
3  3070
4  2898
5  2346
6  2392
7  2212
8  2358
9  2324
10 2330
11 2270
12 2436
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Last fiddled with by fivemack on 2011-03-14 at 23:49
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Old 2011-03-14, 23:43   #2
Batalov's Avatar
Mar 2008

223228 Posts

The Xeon X56x0's (I've had a brief access to one or two of these, both dual and a single X5680) throw a handful of sand into msieve's inner workings by self-reporting their cache sizes strangely - which in turn affects the chosen block size for LA. I've seen that when they ran with block size manually set to 32768 (and compiled without -DLARGEBLOCK), they seemed to scale better.
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