How does Live balance usage of Dual CPUs in OSX?

Tim York · Post by **Tim York** » Wed Aug 13, 2003 10:17 pm

Could someone say how Live uses dual CPUs on a G4 in OSX - both in stand alone and rewired to Logic?

What I have been able to discern is that in OS9 and rewired with Logic 6.1, Live uses processor B entirely.

In OS9 Logic shows dual meters bars for system performance. Therefore I was able to easily work this one out. (Processor B is the left bar).

But in OSX Logic only has one meter bar, so it is impossible to tell. There is a CPU monitor (with two bars) in OSX (part of the OS), but it isn't very accurate.

Tim

fugu · Post by **fugu** » Wed Aug 13, 2003 10:44 pm

I'm fairly certian that OSX manages all (single, dual and soon beyond <que spooky music>...) processor use in OSX, the single meter is representative of the 'total' load (DP4 has the same 'single meter' Logic does). In os9 the individual software application needed to do this using it's own methods in order to take any advantage of the 2nd processor, hence 2 meters. To test this, open the Process Meter in the Utilities folder (top, for you unix geeks) with a nice heavy load on the machine (and i do mean heavy) and you'll commonly see processes using > 100% .. that's more then one processor right there, no muss no fuss. I'm hardly a coder, but my understanding is that Apple has done far more work then the developers (of any application) need to do to make their application most efficiently use 2 processors. .

Using a 1.25 MDD, I've found myself hitting the wall with bus throughput or disk i/o *way* before the processors could ever max out. G5 machines will change this for the better as the system bus is increased ~6-7x (167mhz to 1ghz), but I'd bet that disk i/o and system bus will remain the limiting factors for a while to come....

--hope this helps

Tim York · Post by **Tim York** » Wed Aug 13, 2003 11:32 pm

With Logic there are a couple of tricks to force tracks to use the 2nd CPU. One of these is to put a so called "I/O plug in" on a track, assign it an output, then bypass it. In OS9 you can see the CPU meters change when you do this. In OSX you can see TOP going to a higher figure before the computer craps out. One would conclude from this that Mac OSX is not automatically sharing the load, and neither is Logic in OSX, as these workarounds still make a difference to system performance.

It's a bit of a mystery as to why Emagic decided to take away the 2nd meter bar, which was very useful when applying these workarounds.

Tim

Tim York · Post by **Tim York** » Thu Aug 14, 2003 8:06 pm

Ableton?

Live's use of dual processors in OSX. Stand alone and rewired with Logic. Which processors get used in these two scenarios?

Can you help here please?

Tim

Tim York · Post by **Tim York** » Thu Aug 14, 2003 9:53 pm

Thanks Ableton, I got your email. I'll post it here in case anyone else is interested:

"OS X dynamically allocates tasks to the processor.

Live as standalone: Generally the GUI is handled by one processor and the other tasks by the other processor.

Live as ReWire Slave: The ReWire Master handles the audio engine and the allocation of tasks to the processors. I believe the GUI is still handled by one of the processors."

Tim