CODEWITHSUNDEEP
linuxcpu-usage
Ellen Blauw
Ellen Blauw

Reputation: 31

How to get the CPU information of a process in Linux?

In my server, there exists several CPUs (0-7). I need run parallel code, and each process affiliate with one CPU, so how do I know the CPU information for each process?

For example, if two processes (#0 and #1) exist, and process #0 uses CPU 5 and process #1 uses CPU 7.

how do I know that by programming in C or Fortran?

Upvotes: 3

Views: 2184

Answers (5)

Anycorn
Anycorn

Reputation: 51465

Generally, you have to change the CPU affinity, because a process can migrate between processors: CPU Affinity (Linux Journal, 2003).

Upvotes: 0

Noah Watkins
Noah Watkins

Reputation: 5540

I'm not aware of any system call on Linux that will give you general information about what CPU a thread in running on. @nos is correct that sched_getcpu() will tell you which CPU a thread is running on, but only for the calling context.

You can do this by querying the /proc file system. However, if you find yourself building your application around this functionality, it is likely that you need to reexamine your design.

The file /proc/<pid>/stats contains a field that provides you with the last CPU the process ran on. You would just need to parse the output. (use man proc to see the field list).

Upvotes: 2

nos
nos

Reputation: 229098

Use the sched_getcpu() call.

Keep in mind that a process/thread can be scheduled freely to run on any available cpu/core, so one of your processes could run on core 1 one second, and on core 2 the next milisecond. You can restrict which processors a process is allowed to run on with sched_setaffinity()

Upvotes: 2

Niels Basjes
Niels Basjes

Reputation: 10642

In general it is the task of the operating system to abstract such things from applications. Normally I see my applications (as simple as doing a grep on a huge file) change CPU core every once in a while.

Now if you want to force an application on a specific core you can manually set the CPU affinity.

I've written some pretty strange software in the past and I've never had the desire to know and/or control this.

Why would you want to know?

Upvotes: 1

dty
dty

Reputation: 18998

More generally, why do you want to know? The Linux kernel is very good at scheduling processes/threads to make the best use of the available cores.

Upvotes: 0

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