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How can I go about finding the PID or other information about a process that is doing the work of another process? I'm talking about kworker threads, for example, or any other threads/processes that are doing work within the kernel for another process.

My dilemma is that I have a real-time scheduled process (SCHED_FIFO) running at sched prio 99, with CPU affinity bound to CPU 0, but when I inject CPU stress onto my machine, I notice that my important rt process is not able to preempt the other, non-important processes. I'm thinking this may be because the kworkers that do work for this important process do not inherit the priority that the main process has, even though I specify the -a option in taskset and chrt. My current idea is to manually taskset and chrt the kworker threads so they don't get preempted by other, non-rt processes.

stochasticlover1
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2 Answers2

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You can get a tree of all the tasks started by a process if you know the PID of the starting process using ps.

$ ps f -g2305957
    PID TTY      STAT   TIME COMMAND
2305957 pts/20   Ss     0:00 bash
2310399 pts/20   S+     0:00  \_ stress -t 300 -c 16
2310400 pts/20   R+     0:24      \_ stress -t 300 -c 16
2310401 pts/20   R+     0:24      \_ stress -t 300 -c 16
2310402 pts/20   R+     0:24      \_ stress -t 300 -c 16
2310403 pts/20   R+     0:24      \_ stress -t 300 -c 16
2310404 pts/20   R+     0:24      \_ stress -t 300 -c 16
2310405 pts/20   R+     0:24      \_ stress -t 300 -c 16
2310406 pts/20   R+     0:23      \_ stress -t 300 -c 16
2310407 pts/20   R+     0:25      \_ stress -t 300 -c 16
2310408 pts/20   R+     0:22      \_ stress -t 300 -c 16
2310409 pts/20   R+     0:24      \_ stress -t 300 -c 16
2310410 pts/20   R+     0:25      \_ stress -t 300 -c 16
2310411 pts/20   R+     0:24      \_ stress -t 300 -c 16
2310412 pts/20   R+     0:23      \_ stress -t 300 -c 16
2310413 pts/20   R+     0:24      \_ stress -t 300 -c 16
2310414 pts/20   R+     0:25      \_ stress -t 300 -c 16
2310415 pts/20   R+     0:22      \_ stress -t 300 -c 16

This is stress running across 16 threads. Related to this answer.

A. Que
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pstree -p -H <PID>

The command shows you the complete processtree of your system with all PIDs and highlights your process.

Maybe that helps to find what is going on.

ulrich17
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