[PD] parallelism in pd

Miller Puckette mpuckett at man104-1.ucsd.edu
Wed Apr 17 02:10:41 CEST 2002

My understanding of this is all anecdotal (although I was heavily involved
at the hardware level of all this a few years ago.)   The reason Intel
processors are more likely to outrun available memory is that they have
higher CPU "front side bus" bandwidth than AMD processors, hence the same
memory system will be harder put to keep them happy.  I believe the
current P4 has 3.2 GB/sec FSb bandwidth whereas DDR 2100 memory has 2.1 GB/sec,
so unless you can keep your FSB idle 70% of the time your dual-processor-
plus-DDR2100 system, for example, will be limited by memory bandwidth, and
even in that case memory latency will be greater than for a uniprocessor
since the two CPUs will have to queue for memory accesses.

These considerations probably hold equally for threaded applications and
for multiple process models.


On Tue, Apr 16, 2002 at 03:32:09PM -0700, Andrew (Andy) W.  Schmeder wrote:
> On Tue, 2002-04-16 at 10:24, Miller Puckette wrote:
> > I concur, with a slight spin: Pd is often memory-bound, and most
> > dual-processor systems, especially Intel based ones but also AMD,
> > have their speed limited by memory bandwidth (which is shared between
> > processors.)
> In the interesting of maintaining rigor, I'd like to know if there is
> any hard data to back up this claim.. i.e. profiling which demonstrates
> the memory bandwidth versus CPU restrictions, etc on one or more
> systems.
> (To be fair I suppose this means that we need a standard regression
> test/benchmark for a real-time audio system, PDSpec?)
> The reason I ask is that I'm interested in massively multichannel
> systems.
> Also I am curious as to why Intel would have less memory bandwitdth...
> intution suggests it would depend on the type of system memory used...
> rambus versus SDRAM, etc?
> -andy

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