Process.get_cpu_percent() gives wrong values

[giampaolo]

From steve.ko...@gmail.com on June 06, 2013 14:26:08

What steps will reproduce the problem?  
1. get any valid Process instance
2. call get_cpu_percent on this instance with interval == 0
3. value will be zero, even when the process is not idle 

What is the expected output?  
get_cpu_percent(interval=0) should return values > 0.0 at least some time 

What do you see instead?  
values at 0 

What version of psutil are you using? What Python version?  
I'm using psutil 0.7.1, directly from code.google.com (same from pypi), with 
python 2.7 

On what operating system? Is it 32bit or 64bit version?  
It's an Ubuntu 13.04 64bit 

Please provide any additional information below.  
There are 4 logical CPUs on this system.

Original issue: http://code.google.com/p/psutil/issues/detail?id=390

[giampaolo]

From g.rodola on June 06, 2013 05:30:47

From psutil doc:

> When interval is 0.0 or None compares process times to system CPU 
> times elapsed since last call, returning immediately. In this case 
> is recommended for accuracy that this function be called with at 
> least 0.1 seconds between calls.

That means the very first get_cpu_percent(interval=0) call will produce a 
meaningless value as it has no previous value to compare against.
It therefore means you'll need at least TWO calls in order to produce a 
meaningful result and wait some time between one call and the other.

[giampaolo]

From steve.ko...@gmail.com on June 06, 2013 05:40:39

Thank you for your quick answer Giampaolo. I forgot to tell that several calls, 
for the same process, with 5 sec. intervals, always give 0.
Is it relevant to say that everytime I call get_cpu_percent, I create a new 
instance of Process ?

[giampaolo]

From g.rodola on June 06, 2013 06:04:53

You should not create new Process instance every time. That's the problem.

[giampaolo]

From g.rodola on June 06, 2013 07:08:00

Status: Invalid

[giampaolo]

From steve.ko...@gmail.com on June 06, 2013 07:08:14

Yes, you are right, this was the problem.