Athlon MP vs Athlon XP

Thomas Lovie tlovie at pokey.mine.nu
Thu Nov 8 15:36:08 EST 2001


 
> On Thu, Nov 08, 2001 at 02:28:40PM -0500, Velocet wrote:
> 
> > From what I understood from the useful articles that were 
> posted here, 
> > the cache protocol allows sharing data between the CPUs via the 
> > northbridge directly.
> 
> Right. What it comes down to is this: Getting data from L2 is 
> always fastest if its in your own L2. But if it isn't, some 
> machines fetch from main memory faster than they can fetch a 
> dirty line from someone else's L2. AMD's scheme has 
> reasonably fast main memory fetches, plus even more efficient 
> fetches from a remote L2.
> 
> I believe the Sun E10k is one of the few processors where 
> main memory is closer than someone else's L2. That makes 
> false sharing even worse than usual.
> 
> However, from the beowulf standpoint, most of us are running 
> 2 independent mpi proceses on dual cpu boxes, right?

I have a innocent question.... Does the kernel have processor affinity
built in to it yet?  The situation may arise that one of the mpi
processes gets bumped from it's processor, by a system task, then it in
turn bumps the other mpi task from the other processor, and in effect,
it's info is cached in the other processor.  I see the advantage that
fetching from a remote L2 is better, but does anybody know the status of
assigning a processor affinity mask to processes?

Tom Lovie.

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