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