Messages in this thread | | | Date | Mon, 7 Jun 2004 10:56:25 +0200 | From | bert hubert <> | Subject | BUG in ht-aware scheduler/nice in 2.6.7-rc2 on dual xeon |
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Con, Ingo, List,
I'm overjoyed with decent ht-aware scheduling in 2.6.7-rc2 and it does mostly the right thing. However, the 'nice' work by Con shows some slight problems.
Please find attached program 'eat-time.cc'. Make sure not to compile it with -O which might confuse things as this program basically does nothing.
Run it without arguments to determine the speed of 1 cpu, it outputs a number (megaloops/second). Then start it with that number as a parameter:
Sample:
$ ./eat-time 592 $ ./eat-time 592 99% 99% 100% etc
Now starting four of these at the same time gives the desired result:
$ ./eat-time 592 & ./eat-time 592 & ./eat-time 592 & ./eat-time 592 50% 50% 50% 50% etc
This however:
$ ./eat-time 592 & ./eat-time 592 & 100% 99% In another xterm: $ nice -n +19 ./eat-time 592 & nice -n +19 ./eat-time 592 5% 5% 5%
Fails sometimes, with all processes getting 50%. The above 'screenshot' is from the working and expected situation, which happens most of the time.
When it goes wrong, top shows me that Cpu0 and Cpu1 are 100% user, while Cpu2 and Cpu3 are both 100% nice. The niced processes show up in top as PRiority 39, the unniced ones (NI = 0) as PR 25.
I've also seen it that Cpu2 and Cpu3 are 100% busy, and 0 and 1 are 100% nice.
I'd say this situation happens once every 5 or 8 invocations, and perhaps somewhat more when first starting the niced processes.
Perhaps related, when running the above 'nice -n +19' line on its own, I see all CPUs getting load over time, the two processes are wandering. After a while they settle down, only to go on wandering again some time later, also touching configurations where a physical cpu suddenly hosts two processes.
Without nice, two processes get firmly pegged to different physical CPUs.
Anything I can do to help resolve this, just yell.
Thanks!
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