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bashshelltaskaffinity

Commutative property of the commands

I need to ask this question just to double check the answer.

Does the order of the commands matter? For example:

Is this command

 taskset 0x2 time echo "foo"

equal than

time taskset 0x2 echo "foo"

?

I need to know if all the commands followed by the taskset will have the same CPU affinity or just the command immediately after it.

Solution

  • I need to know if all the commands followed by the taskset will have the same CPU affinity or just the command immediately after it.

    Here is a little experiment:

    Start two BG tasks

    $ > taskset 0x2 sleep 50 & sleep 60 &

    Get their PIDs

    $ > ps
  PID TTY          TIME CMD
18562 pts/81   00:00:00 bash
20750 pts/81   00:00:00 sleep
20751 pts/81   00:00:00 sleep
20752 pts/81   00:00:00 ps

    Get the CPU affinity of the known PIDs:

    $ > taskset -p 20750
pid 20750's current affinity mask: 2
$ > taskset -p 20751
pid 20751's current affinity mask: 3f

    So, it seems like the CPU affinity is set for the first process only.

    Update (trying to explain the following behavior):

    1. /usr/bin/time taskset 0x2 sleep 100000=> only sleep gets the affinity mask 2 (somewhat expected!)
    2. taskset 0x2 /usr/bin/time sleep 100000 => both time and sleep get the affinity mask 2 (need to clarify!)

    In the second case, let's call ps -f to get the PPID (parent PID) for each process:

    $> taskset 0x2 /usr/bin/time sleep 60 &
[1] 5942
$> ps -f
UID        PID  PPID  C STIME TTY          TIME CMD
user      5942  9698  0 18:19 pts/261  00:00:00 /usr/bin/time sleep 60
user      5943  5942  0 18:19 pts/261  00:00:00 sleep 60
user      5944  9698  0 18:19 pts/261  00:00:00 ps -f
user      9509  9508  0 16:19 pts/261  00:00:00 -bash
user      9698  9509  0 16:20 pts/261  00:00:00 bash
$> taskset -p 5942
pid 5942's current affinity mask: 2
$> taskset -p 5943
pid 5943's current affinity mask: 2

    What can be seen is that sleep's PPID (5942) corresponds to /usr/bin/time's PID (5942). IOW sleep is a child process of (has been forked from) /usr/bin/time. Because any child process inherits the configuration of the parent process, sleep will have the same CPU affinity with /usr/bin/time.