Messages in this thread | | | Date | Wed, 31 Aug 2005 21:59:40 +1000 | From | Nick Piggin <> | Subject | Re: strange CPU speedups with SMP on Athlon 64 X2 |
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Nathan Becker wrote: > > I would be happy to post my exact C source that I use to do the > benchmark, but I wanted to get some feedback first in case I'm just > doing something stupid. Also, since I'm not subscribed to this list, > please cc me directly regarding this topic. >
Hi Nathan,
Cache issues may explain this. When 2 processes are allocating memory in parallel they'll be given different interleavings of pages which could explain the speedup.
Start one process, get it to memset all its memory, then pause it and do the same thing. Then set them both running at the same time (ie. after they've each touched their memory in turn), what do you see?
(By memset()ing the memory, you'll cause the kernel to actually allocate a physical page. By doing that one after the other, we hope to eliminate interleaving issues.)
-- SUSE Labs, Novell Inc.
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