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On Linux, how do I the check CPU affinity of a process and its threads?

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Why are you doing this? For a multithreaded process where you care about affinity, couldn't you use taskset to execute or leverage cgroups so the children all respect the affinities? – ewwhite Jan 2 '13 at 23:27
@ewwhite I'm doing this to check the affinity after setting them. I'm not asking about how or why to set the affinity. – JamesThomasMoon1979 Feb 7 '13 at 0:10
O I C... Actually, not really. You haven't explained why you're looking for this info. – ewwhite Feb 7 '13 at 0:27
@ewwhite The why is to verify a program's threads have affinity set as expected. These are mostly-independent processing threads on a multicore machine. – JamesThomasMoon1979 Feb 8 '13 at 6:04

1 Answer 1

It's pretty simple. Gather the all process id and thread ids, then call taskset.

pname="apache2" # for example
for pid in $(pgrep "${pname}") ; do 
    [ "${pid}" != "" ] || exit
    echo "PID: ${pid}"
    for tid in \
          $(ps --no-headers -ww -p "${pid}" -L -olwp | sed 's/$/ /' | tr  -d '\n') ; do
        taskset -cp "${tid}"  # substitute thread id in place of a process id

The reason this is not a simple one-liner is because the pgrep command cannot return thread ids (only process ids). We do a little extra work with the command ps --no-headers -ww -p "${pid}" -L -olwp

Tested on Ubuntu 12, bash 4.

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