CPU affinity

Anthony · #1 January 24th, 2004, 02:37 PM

On a multi-processor Windows NT based machine you can bring up task manager, look at the list of running processes, right click and use the "Set Affinity" option to tell which processes to use which CPU. I'm wondering if there is something equivalent on OS X so that I could force certain processes to use certain CPUs and override the automatic threading/affinity. Any ideas? Or is it not even possible on the Darwin kernel?

**Cheryl** · #2 January 25th, 2004, 07:32 AM

Check out the Process Viewer in Utilities.

Anthony · #3 January 25th, 2004, 08:22 AM

I've already looked that over but can't find anything to do with affinity.. it doesn't even display information related to which CPU is doing what other than the overall load on each. I also noticed the unix command "pset" is missing from Unix side that would normally let you set the affinity, so I'm thinking maybe Darwin doesn't support on-the-fly changes in this manner. (Its entirely possible, I don't think Linux supports it either without special kernel hacks.)

crash · #4 January 25th, 2004, 09:39 AM

isn't this also called "nice"? like, you can re-nice a process to allot more cpu? maybe i'm wrong.

bobw · #5 January 25th, 2004, 09:46 AM

man nice

http://www.versiontracker.com/dyn/moreinfo/macosx/9473

http://www.versiontracker.com/dyn/moreinfo/macosx/13336

http://www.versiontracker.com/dyn/moreinfo/macosx/13366

Anthony · #6 January 25th, 2004, 10:05 AM

Its not the same thing as nice. CPU affinity means selecting WHICH cpu does which thread. Its only something you consider on multiple-cpu machines. Nice changes the priority of a PROCESS. Processes are made up of one or more threads. Affinity is which physical CPU processes which thread. The system kernel automatically distributes threads across multiple CPUs but sometimes it doesn't do the most efficient job.

For example if I'm encoding a large video file (which is something I do quite often, the main reason I'm trying to figure out if this is possible), I could have a thread running for literally 10-20 hours. The thread is assigned to a CPU at the beginning of the task, which might make sense at the time... but after many hours depending on what else I'm doing on my machine it might not make sense to still be running it on that CPU. Its a nerdy nit-picky thing, but it would just be nice to be able to shuffle things around so that I'm getting the most out of the machine when I'm running these really long and intensive tasks.

crash · #7 January 25th, 2004, 09:53 PM

in that case, an alternate solution might be to take a look at apples xGrid app. if you have multiple macs, it might make sense to let the large time-intensive task be distributed to other machines on your network.though, i suppose if you had a mac sitting around, you wouldn't be asking this question.