topic If you're looking for an in Intel® MPI Library

Setting affinity for third party applications that create threads

dehvidc1 — Tue, 25 Mar 2014 02:24:16 GMT

Hope this is the correct forum to ask this question.

We can use KMP_AFFINITY and associated infrastructure to set affinity for threads spawned by applications we've developed. And we can use numactl to bind a single-process third-party application to a core. What's available to bind threads spawned by a third-party process to a particular core? We can set what's effectively a CPU set using numactl for a third-party application. The threads spawned by a third-party process will stay within this CPU set but appear to move around between cores. I would be grateful for pointers on how we can bind threads spawned by a third-party process to a particular core

Thanks

David

hello David,

Vladimir_P_1234567890 — Tue, 08 Apr 2014 09:25:28 GMT

hello David,

you can use affinity API to pin 3rd party threads to cores:

sched_setaffinity() for linux, cpuset_setaffinity() for FreeBSD or SetThreadGroupAffinity() for windows.

--Vladimir

Do you mean there is a

TimP — Tue, 08 Apr 2014 09:47:38 GMT

Do you mean there is a requirement not to link against libgomp or libiomp? taskset may be of use

Thanks for the replies. My

dehvidc1 — Tue, 08 Apr 2014 23:50:05 GMT

Thanks for the replies. My problem is how I can set affinity to cores with third-party applications. These are applications for which I don't have the code so I can't compile and link them.

Is there any way to fix a thread to a core for threads spawned by a third-party application for which the source code is unavailable?

Thanks

David

From outside of a process,

James_T_Intel — Wed, 09 Apr 2014 13:27:10 GMT

From outside of a process, you're really only going to be able to control the affinity of the entire process. Depending on how the application spawns its threads, you *might* be able to bind the process to the desired core, let the application spawn the thread, and then move the main process. I don't really expect that to work, but it might be worth exploring if you absolutely have to pin the applications threads to individual cores.

If you're looking for an

TimP — Wed, 09 Apr 2014 14:13:03 GMT

If you're looking for an answer which is independent of which OS, MPI and threading model is used in the application, I think you're out of luck. Your reference to numactl would seem to indicate linux with pthreads, in which case you could set up a separate taskset selection for each MPI process, giving each process a selection of hardware contexts, with an effect similar to what you would get by setting KMP_AFFINITY for each process when libiomp is in use.

I don't see you explaining why you like numactl for a single-process application but not for multiple processes. I suppose numactl or taskset may be applicable only for MPI_THREAD_FUNNELED model, but you didn't say explicitly that you have something different in mind.

I guess you may not have meant to ask for an equivalent to KMP_AFFINITY which works for any pthreads application. Standard equivalents to KMP_AFFINITY are OMP_PROC_BIND and OMP_PLACES, but I'm sure you could find applications built not so long ago against libraries not sufficiently up to date to support them.