taskset - python

Question

I have a dual quad core machine. so, the cpu list for me 0-7.

I am trying to run the taskset from python

mapping = [2,2,2,2,2]
for i in range(0,len(mapping)):
        cmd = "taskset -c" +  str(mapping[r]) + "python <path>/run-apps.py" + thr[r] + "&"
        os.system(cmd)

and it says:

taskset: invalid option -- '2'
taskset (util-linux-ng 2.17.2)
usage: taskset [options] [mask | cpu-list] [pid | cmd [args...]]
set or get the affinity of a process

  -p, --pid                  operate on existing given pid
  -c, --cpu-list             display and specify cpus in list format
  -h, --help                 display this help
  -V, --version              output version information

The default behavior is to run a new command:
  taskset 03 sshd -b 1024
You can retrieve the mask of an existing task:
  taskset -p 700
Or set it:
  taskset -p 03 700
List format uses a comma-separated list instead of a mask:
  taskset -pc 0,3,7-11 700
Ranges in list format can take a stride argument:
  e.g. 0-31:2 is equivalent to mask 0x55555555

But the core 2 is available and I am to run the same thing from commandline.

taskset -c 2 python <path>/run-apps.py lbm &

not a clue what the issue is..

any hints?

Answer 1

You can avoid calling taskset and use psutil instead: https://pythonhosted.org/psutil/#psutil.Process.cpu_affinity

>>> import psutil
>>> psutil.cpu_count()
4
>>> p = psutil.Process()
>>> p.cpu_affinity()  # get
[0, 1, 2, 3]
>>> p.cpu_affinity([0])  # set; from now on, process will run on CPU #0 only
>>> p.cpu_affinity()
[0]
>>>
>>> # reset affinity against all CPUs
>>> all_cpus = list(range(psutil.cpu_count()))
>>> p.cpu_affinity(all_cpus)
>>>

Answer 2

compared to the commandline you posted, you're missing a couple spaces ... e.g.:

cmd = "taskset -c " +  str(mapping[r]) + " python <path>/run-apps.py " + thr[r] + " &"

In your code, when parsing the "commandline", taskset is seeing the string -c2 which according to many commandline parsing libraries is the same thing as -c -2 which would explain the error that you're seeing.

Sometimes these things are easier to read if you use string interpolation instead:

cmd = "taskset -c %s python <path>/run-apps.py %s &" % (mapping[r],thr[r])

Or new style .format:

cmd = "taskset -c {0} python <path>/run-apps.py {1} &".format(mapping[r],thr[r])

And finally, no solution using os.system should go by without at least a mention of the python subprocess module.

process = subprocess.Popen(['taskset',
                            '-c',
                            str(mapping[r]),
                            'python',
                            '<path>/run-apps.py',
                            str(thr[r]) ] )

It'll avoid the shell altogether which is slightly more efficient and makes you safer from shell injection types of attacks.