What core is a given thread running on?

Question

Is there a function or any other way to know, programatically, what core of what processor a given thread of my program (pid) is running on? Both OpenMP or Pthreads solution

Answer 1

For pthreads, I think sched_getaffinity() is at least part of the solution. Not sure exactly how pthreads names the CPU:s and cores, though.

Answer 2

This is going to be platform-specific, I would think. On Windows you can use NtGetCurrentProcessorNumber, but this is caveat-ed as possibly disappearing.

I expect this is hard to do, because there's nothing to stop the thread being moved to a new core at any time (in most apps, anyway). As soon as you get the result, it could be out of date.

Answer 3

I think on Linux one can try sched_getcpu().

Answer 4

This is hard to do portably, as the answer depends both on hardware and OS.

The hardware locality library is a new tool which allows you to query CPU/core/thread etc information (and set affinity bindings) in an OS/hardware agnostic way. It supports a huge list of hardware and OSes, and so should add a lot of portability to these sorts of queries. Once you map out your system's topology, hwloc_get_last_cpu_location will return the CPU the thread last ran on, where CPU can mean core or hardware thread.