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How can I set the processor affinity of a process on Linux?

23

I have used taskset for this. If you have taskset installed, something like:

taskset -c 1,3 -p 45678

would set the process with id 45678 to have an affinity to cpus 1 and 3.

  • 1
    An anonymous edit suggested that the command must be taskset -p -c 1,3 45678 rather than taskset -c 1,3 -p 45678; i.e., that the -c 1,3 is a mask specification and, as such, must be placed between the -p and the pid. – G-Man Oct 14 '18 at 19:27
7

Inside the process, the call would be sched_setaffinity(), or for pthreads stuff, pthread_setaffinity_np()

On a related note, if you're worrying about CPU affinity of your program, it may be worthwhile to pay attention to how it's doing memory allocation as well. Larger systems with memory attached to more than one controller (i.e. multiple CPU sockets, each with their own) will have variable latency and bandwidth between different CPU-memory pairs. You'll want to look into NUMA affinity as well, using the numactl command or the system calls that it works with. One program I worked on got a 10% performance improvement from this.

3

You need to install schedutils (Linux scheduler utilities). I have use it on my Ubuntu Desktop.

SF link

1
taskset -c 1-3 ./a.out arg1 arg2

launches the a.out process with given arguments and affinity set to processors 1, 2 or 3 (zero based).

Here is a minimal C test program that can be used to see it in action: https://stackoverflow.com/questions/10490756/how-to-use-sched-getaffinity-and-sched-setaffinity-in-linux-from-c/50117787#50117787

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