[PD] pd and multi-core processors

Tim Blechmann tim at klingt.org
Wed Apr 7 09:30:34 CEST 2010

>> the average cpu load won't tell you a lot, since the cpu speed is usually
>> not constant, but may be modulated (adding some latency hotspots). in
>> general, i'd recommend to disable frequency scaling, turbo mode (for
>> nehalem
>> cpus) and smt, since it may confuse numbers and can increase the thread
>> wakeup latency significantly, if you want to use a machine for
>> low-latency real-time audio applications.
> thanks for the tip. I have no idea how to do that though.
> I admit not having searched for very long (it's late), but i couldn't find
> an easy peasy how-to disable frequency scaling, or about that turbo mode
> and smt stuff...
> maybe you (or someone else) can explain this in a bit more detail?

usually these are bios options. the basic idea for disabling this stuff is 
to avoid system-level interrupts, that could introduce considerable wakeup 
latencies in the worst case.

>> > so, still plenty of overhead on the 4th core, but it doesn't seem to be
>> > used.
>> from my understanding, you should split your path into 4 pieces of equal
>> load, using 3 pd~ objects, if you want to optimize it for a quad-core
>> cpu.
> hmm, if I try to load one patch into a pd~ object I get garbled sound,
> even without switch~ing it on.
> Would you think if I split off more of my main patch into more pd~ objects
> it would improve ?
> The fact that using pd~ results in more hickups than a normal abstraction
> leads me to suspect something else is wrong...

if your patch works fine on a single cpu, but not with pd~, i would also 
suspect, that something else is going wrong. there could be various reasons 
for the hickups like scheduling issues, buffer synchronization issues and 
the like.
however, i have no insight in the implementation of pd~, but since pd~ is 
part of vanilla pd, i am sure, miller will be interested in resolving all 
issues, that pd~ may have.

cheers, tim

tim at klingt.org

A year ago, six months ago, I thought that I was an artist. I no 
longer think about it, I am.
  Henry Miller

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