Bug 114987 - Very poor task switching on average load
Very poor task switching on average load
Product: Red Hat Linux
Classification: Retired
Component: kernel (Show other bugs)
athlon Linux
medium Severity high
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Assigned To: Ingo Molnar
Brian Brock
Depends On:
  Show dependency treegraph
Reported: 2004-02-05 00:57 EST by Nicolas Barry
Modified: 2007-04-18 13:02 EDT (History)
1 user (show)

See Also:
Fixed In Version:
Doc Type: Bug Fix
Doc Text:
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Clone Of:
Last Closed: 2004-08-18 07:41:47 EDT
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Regression: ---
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oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

Attachments (Terms of Use)
Source code of test program (2.98 KB, text/plain)
2004-02-05 00:58 EST, Nicolas Barry
no flags Details
Watchdog script : detects lags of more than 2 seconds (167 bytes, text/plain)
2004-02-05 15:05 EST, Nicolas Barry
no flags Details

  None (edit)
Description Nicolas Barry 2004-02-05 00:57:09 EST
Description of problem:
We have a set of multithreaded processes running on Redhat 9 machines.
When there is some load, it seems that only a few threads inside
certain processes get to be executed in a fair way. Certain threads,
in particular watchdog threads, that sleep most of the time, timeout
the entire system.
This problem does not occur on a stock 2.4.x kernel, we tried the
latest development 2.4 kernel, and couldn't reproduce the problem.

I tested this problem on a variety of systems, one is an athlon single
processor, and pentium 3 single and dual processor.

Version-Release number of selected component (if applicable):
2.4.20-27.9 or any 2.6.1 through 2.6.2 kernels

How reproducible:
Very easily using the test program combined with the watchdog script.

Steps to Reproduce:
0. Compile cputest with gcc -pthread -D_REENTRANT -lm cputest.c -o cputest
1. Start the watchdog script in a shell
2. Start the test program: ./cputest 20 10000 1000 512 
3. Watch the output of the watchdog script
Actual results:
An output that looks like
>>>>>>> delta = 3 Tue Jan 27 15:31:22 PST 2004
>>>>>>> delta = 4 Tue Jan 27 15:31:27 PST 2004
>>>>>>> delta = 4 Tue Jan 27 15:31:34 PST 2004
>>>>>>> delta = 6 Tue Jan 27 15:31:54 PST 2004
>>>>>>> delta = 6 Tue Jan 27 15:32:04 PST 2004
>>>>>>> delta = 20 Tue Jan 27 15:32:13 PST 2004
meaning, in that case, that I got a 20 seconds "freeze" of the
watchdog script that ended at 15:32:13

Expected results:
There should be no freezes like this, regardless of the load, as the
watchdog script needs a very minimal number of cycles to execute every

Additional info:
Comment 1 Nicolas Barry 2004-02-05 00:58:48 EST
Created attachment 97484 [details]
Source code of test program
Comment 2 Dave Jones 2004-02-05 13:41:47 EST
Can you attach the watchdog script too please?
Comment 3 Nicolas Barry 2004-02-05 15:05:27 EST
Created attachment 97498 [details]
Watchdog script : detects lags of more than 2 seconds

Forgot to post the watchdog script earlier

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