Bug 187748 - Problemes with sceduling
Summary: Problemes with sceduling
Alias: None
Product: Red Hat Enterprise Linux 3
Classification: Red Hat
Component: kernel   
(Show other bugs)
Version: 3.0
Hardware: i386
OS: Linux
Target Milestone: ---
Assignee: Ingo Molnar
QA Contact: Brian Brock
Depends On:
TreeView+ depends on / blocked
Reported: 2006-04-03 13:49 UTC by Klaus Ethgen
Modified: 2007-11-30 22:07 UTC (History)
2 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
Last Closed: 2007-10-19 18:45:33 UTC
Type: ---
Regression: ---
Mount Type: ---
Documentation: ---
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

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Description Klaus Ethgen 2006-04-03 13:49:24 UTC
Description of problem:
With the EL3 (WS3) release the sceduler do not handle nice processes propper
on a smp system.

Here is a snipplet of the process state:
CPU states: cpu user nice system irq softirq iowait idle
total 99.8% 100.0% 0.0% 0.0% 0.0% 0.0% 0.0%
cpu00 0.0% 100.0% 0.0% 0.0% 0.0% 0.0% 0.0%
cpu01 99.9% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0%

22143 darwin 39 19 54436 53M 42304 R N 50.0 10.6 7:36 0 darwin
21249 darwin 39 19 58460 57M 42300 R N 49.9 11.4 21:51 0 darwin
22431 darwin 25 0 147M 147M 104M R 49.9 29.6 3:51 1 darwin
21676 darwin 25 0 46220 45M 384 R 49.8 9.0 9:46 1 darwin

As you can see the nice processes sitts on one CPU and the non nice on the
other. This is wrong and can only be found in the 2.4 kernel of redhat. The
vanilla kernel do correct.

With the above processes the nice processes should not get 50% of all CPU power

Version-Release number of selected component (if applicable): 2.4.x

How reproducible:
This bug is hardely to reproduce as it only appere sometimes.

I did a small programm to test it but I cannot prove that this will show the bug:
#include <stdio.h>
#include <unistd.h>

int main(int argc, char **argv)
   unsigned long pid;

   if ((pid = fork()) == 0)
      for (;;);
   if ((pid = fork()) == 0)
      for (;;);
   if ((pid = fork()) == 0)
      for (;;);
   for (;;);
   return 0;
} // int main(int argc, char **argv...

I did some research and found that you just apply the O(1) patch to your 2.4.x
kernels. I think this bug is somewhat buggy and make more problemes than
solving. But I'm not absolutely sure that this is the problem.

Comment 1 Gaston Gonnet 2006-04-12 20:54:39 UTC
Let me add some additional info to the above.  The problem is difficult to reproduce because it requires 
two cpus and 4 process (2 normal and 2 niced) to show up.  Then it will happen when the 2 niced 
processes are assigned to one cpu and the 2 non-niced processes are assigned to the other cpu. All the 
processes then get 50% of the cpu.  In all other kernels this is recognized or rotated sufficiently often 
so that it does not become a problem.  In the long run the niced processes get about 10% of the cpu.  
In 2.4 they stay like that forever.  This is serious in our setup where we *always* have processes 
running in the background at low priority (niced).  Best wishes, Gaston Gonnet.

Comment 2 RHEL Product and Program Management 2007-10-19 18:45:33 UTC
This bug is filed against RHEL 3, which is in maintenance phase.
During the maintenance phase, only security errata and select mission
critical bug fixes will be released for enterprise products. Since
this bug does not meet that criteria, it is now being closed.
For more information of the RHEL errata support policy, please visit:
If you feel this bug is indeed mission critical, please contact your
support representative. You may be asked to provide detailed
information on how this bug is affecting you.

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