Red Hat Bugzilla – Bug 114987
Very poor task switching on average load
Last modified: 2007-04-18 13:02:33 EDT
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
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
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
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
Created attachment 97484 [details]
Source code of test program
Can you attach the watchdog script too please?
Created attachment 97498 [details]
Watchdog script : detects lags of more than 2 seconds
Forgot to post the watchdog script earlier