Dual processor, AMD 64 machine freezing.

David O'Brien obrien at freebsd.org
Sun Feb 1 16:53:30 PST 2004

On Mon, Feb 02, 2004 at 12:51:34AM +0100, Andreas Braukmann wrote:
> > P.S. For best performance, I think you really want to run 4x 512 MB.
> > Running with two DIMMs means either you only get 64-bit memory access (not
> > 128-bit) or else you need to put both DIMMs into the CPU1 memory slots
> > (which means CPU2 will have to access those through hypertransport).
> Thats theory. ;-)
> Since the allocators don't know about the numa-like architecture
> memory would be accessed through hyptertransport (statistically)
> more or less "half of the time". (CPU0 ---> HT ---> MEM1 ; 
> CPU1 ---> HT ---> MEM0)

Its not theory, its fact -- even w/o a NUMA aware OS.  Statistically, 1/2
the accesses by a CPU are to local memory, 1/2 to distant memory.  If you
put all them memory on a single CPU then you've got two processors trying
to access memory, saturating the memory controller on the single CPU with
memory -- thus giving you less BW.  Your diagram above leaves out the
memory controller (and its request buffer).

-- David  (obrien at FreeBSD.org)
P.S. I work at AMD

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