CODEWITHSUNDEEP
linuxkernel
Jangwoong Kim
Jangwoong Kim

Reputation: 180

how can i get the CPU number of current task (In kernel)?

Is there any way to get CPU number of current task? (What I need is not the number of CPUs the task is running on, but which CPU the task is running on)

This process must be in kernel-level, therefore something like command line won't help.

I am trying to do this by calling kernel functions or using kernel data structures(like task_struct), but I am having trouble.

Upvotes: 4

Views: 2301

Answers (3)

Mohammad Siavashi
Mohammad Siavashi

Reputation: 1262

A rather old question but this might be helpful for the future:

If you have CONFIG_THREAD_INFO_IN_TASK enabled (which is usually the default) then you can simply access the current CPU of the task using the cpu member of task_struct: current->cpu

As you can find in the source:

#ifdef CONFIG_THREAD_INFO_IN_TASK
    /* Current CPU: */
    unsigned int            cpu;
#endif

And also the previous CPU of the task as could be found in task_struct:

    /*
     * recent_used_cpu is initially set as the last CPU used by a task
     * that wakes affine another task. Waker/wakee relationships can
     * push tasks around a CPU where each wakeup moves to the next one.
     * Tracking a recently used CPU allows a quick search for a recently
     * used CPU that may be idle.
     */
    int             recent_used_cpu;

You may also use cpu = task_cpu(p) which return id of the CPU.

Each task is also associated with a runqueue of a CPU. and each runqueue has a cpu field. The runqueue could be simply retrieved by rq = task_rq(p) and then rq->cpu.

Upvotes: 2

rajaganesh87
rajaganesh87

Reputation: 99

CPU details of processes are in /proc/[pid]/stat 39th field gives last CPU number where it was executed.

(39) processor %d (since Linux 2.2.8) CPU number last executed on.

For more details: http://man7.org/linux/man-pages/man5/proc.5.html

Upvotes: -1

steve
steve

Reputation: 183

The sched_getcpu() "determine CPU on which the calling thread is running" function appears to exist solely to provide this.

http://man7.org/linux/man-pages/man3/sched_getcpu.3.html

Upvotes: 0

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