fstat bug?

[Laszlo Nagy]

   Hi All,

I have a Python program that goes up to 100% CPU. Just like this (top):

   PID USERNAME       THR PRI NICE   SIZE    RES STATE   C   TIME   WCPU 
COMMAND
80212 user1           2  44    0 70520K 16212K select  1   0:30 100.00% 
/usr/local/bin/python process_updates_ss_od.py -l 10

I have added extra logs and it turns out that there are two threads. One 
thread is calling "time.sleep()" and the other is calling "os.stat" 
call. (Actually it is calling os.path.isfile, but I hunted down the last 
link in the chain.) The most interesting thing is that the process is in 
"SELECT" state. As far as I know, CPU load should be 0% because "select" 
state should block program execution until the I/O completes.

I must also tell you that the os.stat call is taking long because this 
system has about 7 million files on a slow disk under heavy load. It 
would be normal for an os.stat call to return after 10 seconds. I have 
no problem with that. But I think that the 100% CPU is not acceptable. I 
guess that the code is running a system call in kernel mode. I think 
this because I can send a KILL signal to it and the state changes to the 
following:

   PID USERNAME       THR PRI NICE   SIZE    RES STATE   C   TIME   WCPU 
COMMAND
80212 user1           2  44    0 70520K 15256K STOP    5   1:27 100.00% 
/usr/local/bin/python process_updates_ss_od.py -l 10

So the state of the process changes to "STOP", but the program does not 
stop until the os.stat call returns back. Sometimes for a minute.

Could it be a problem with the operation system? Is it possible that an 
os.stat call requires 100% CPU power from the OS? (I believe that 
os.stat ends in fstat()). Or is it a problem with the Python implementation?

(Unfortunately I cannot give you an example program. Giving an example 
would require giving you a slow I/O device with millions of files on it.)

OS version: FreeBSD 8.1-STABLE amd64
Python version: 2.6.6

Thanks,

    Laszlo


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