Is it possible to tell whether a process/thread has the PF_NO_SETAFFINITY flag set? I'm running taskset on a series of process ids and some are throwing errors of the following form:
taskset: failed to set pid 30's affinity: Invalid argument
I believe this is because some processes have PF_NO_SETAFFINITY set (see Answer).
Thank you!
Yes - look at /proc/PID/stat's 'flag' field
<linux/sched.h
#define PF_NO_SETAFFINITY 0x04000000 /* Userland is not allowed to meddle with cpus_allowed */
Look here for details on using /proc:
Example:
ps -eaf
www-data 30084 19962 0 07:09 ? 00:00:00 /usr/sbin/apache2 -k start
...
cat /proc/30084/stat
30084 (apache2) S 19962 19962 19962 0 -1 4194624 554 0 3 0 0 0 0 0 20 0 1 0 298837672 509616128 5510 18446744073709551615 1 1 0 0 0 0 0 16781312 201346799 0 0 0 17 0 0 0 0 0 0 0 0 0 0 0 0 0 0
The flags are 4194624
Q: Do you mind specifying how you'd write a simple script that outputs true/false based on whether you're allowed to set affinity?
A: I don't feel comfortable providing this without the opportunity to test, but you can try something like this...
flags=$(cut -f 9 -d ' ' /proc/30084/stat)
echo $(($flags & 0x40000000))