psutil.cpu_percent does not work as advertised

[giampaolo]

From philip.r...@gmail.com on June 03, 2011 04:23:02

What steps will reproduce the problem?  
1. Call psutil.cpu_percent(interval=0) multiple times. 

What is the expected output?  


What do you see instead?  
Expected: each call should give cpu usage since previous call.
Actual: gives cpu usage since module import. 

Please provide any additional information below.  
I think this fixes the problem:

Index: psutil/__init__.py
===================================================================
--- psutil/__init__.py  ( revision 980 )
+++ psutil/__init__.py  (working copy)
@@ -601,7 +601,7 @@
     t2_all = sum(t2)
     t2_busy = t2_all - t2.idle

-    _last_cpu_times = t1
+    _last_cpu_times = t2
     # this usually indicates a float precision issue
     if t2_busy <= t1_busy:
         return 0.0

Original issue: http://code.google.com/p/psutil/issues/detail?id=168

[giampaolo]

From g.rodola on June 03, 2011 00:34:42

> Expected: each call should give cpu usage since previous call.
> Actual: gives cpu usage since module import.

I think you're misinterpreting the code.
This is true only *the first time* the function is called.
Since then times are compared against previous function call.

[giampaolo]

From jlo...@gmail.com on June 03, 2011 09:28:11

The current code looks like this:

   if blocking:
        t1 = cpu_times()
        time.sleep(interval)
    else:
        t1 = _last_cpu_times

    t1_all = sum(t1)
    t1_busy = t1_all - t1.idle

    t2 = cpu_times()
    t2_all = sum(t2)
    t2_busy = t2_all - t2.idle

    _last_cpu_times = t1

So if you are using the non-blocking code, it looks like we set t1 = 
_last_cpu_times and then later we are setting _last_cpu_times = t1 without 
modifying it, so it's effectively a no-op. I guess this got introduced when 
adding the blocking code path.

[giampaolo]

From g.rodola on June 03, 2011 10:16:03

You guys are right, sorry.
This is now fixed in r981 .

Status: FixedInSVN
Labels: Milestone-0.2.2

[giampaolo]

From g.rodola on June 27, 2011 10:52:41

Labels: Milestone-0.3.0

[giampaolo]

From g.rodola on July 08, 2011 12:07:35

Status: Fixed

[giampaolo]

From g.rodola on March 02, 2013 04:00:43

Updated csets after the SVN -> Mercurial migration: r981 == revision 
a415d2627242