Finding cpu time spent on my program

[jm.suresh]

I am trying to measure the time the processor spends on some
operation, and I want this measure to not depend on the current load
of the machine. But doing the following prints different values each
time a run.

import time
c1 = time.clock()
for x in xrange(0xFFFFF): pass

c2 = time.clock()
print "Time spent is %f" % (c2-c1)

Is there a way to measure the number of cpu cycles spent on my program
alone irrespective of the current load etc of the machine.

-
Suresh

 

[kyosohma]

I am trying to measure the time the processor spends on some
operation, and I want this measure to not depend on the current load
of the machine. But doing the following prints different values each
time a run.

import time
c1 = time.clock()
for x in xrange(0xFFFFF): pass

c2 = time.clock()
print "Time spent is %f" % (c2-c1)

Is there a way to measure the number of cpu cycles spent on my program
alone irrespective of the current load etc of the machine.

-
Suresh

One of the best ways to time small snippets of code is python's timeit
module. See the docs at http://docs.python.org/lib/module-timeit.html

- Mike

 

[Carl J. Van Arsdall]

There's an performance testing suite that you might also find useful.
Check out TAU: Tuning and Analysis Utilities toolkit (simple google
search will take you to the page). You can get some serious numbers
using that thing and they have python support as well as some tools for
automatically profiling an entire application. Check it out.

-carl

--

Carl J. Van Arsdall
(e-mail address removed)
Build and Release
MontaVista Software

 

[Nick Craig-Wood]

One of the best ways to time small snippets of code is python's timeit
module. See the docs at
http://docs.python.org/lib/module-timeit.html

Timeit is very cool, but it doesn't measure CPU time, it measure real
time, eg on a linux box

$ python -m timeit 'for i in xrange(100000): pass'
100 loops, best of 3: 11.4 msec per loop

Now run 10 copies of the same program at once

$ for i in `seq 10` ; do python -m timeit 'for i in xrange(100000): pass' & done
10 loops, best of 3: 24.4 msec per loop
10 loops, best of 3: 83.2 msec per loop
10 loops, best of 3: 83.4 msec per loop
10 loops, best of 3: 81.4 msec per loop
10 loops, best of 3: 83 msec per loop
10 loops, best of 3: 60.7 msec per loop
10 loops, best of 3: 47 msec per loop
10 loops, best of 3: 48.6 msec per loop
10 loops, best of 3: 42.3 msec per loop
10 loops, best of 3: 38.7 msec per loop

The most accurate way of measuring CPU usage under linux is getrusage,
eg
.... return resource.getrusage(resource.RUSAGE_SELF)[0]
....

Now try this out
.... for i in xrange(100000):
.... pass
.... 0.008001

You'll see the result is quantised to 4 ms (not sure what the .000001
bits are about!)

4ms is the clock rate of this machine, ie 250 Hz. This is a compile
time option for the linux kernel and is usually set in the range 100
Hz to 1000 Hz. The kernel doesn't measure CPU usage more accurately
than this.