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    SubjectRe: [patch] CFS scheduler, -v18
    Hi Ingo,

    On Sun, Jun 24, 2007 at 05:52:14PM +0200, Ingo Molnar wrote:
    >
    > * Willy Tarreau <w@1wt.eu> wrote:
    >
    > > Today I had a little time to try CFS again (last time it was -v9!). I
    > > ran it on top of 2.6.20.14, and simply tried ocbench again. You
    > > remember ? With -v9, I ran 64 processes which all progressed very
    > > smoothly. With -v18, it's not the case anymore. When I run 64
    > > processes, only 7 of them show smooth rounds, while all the other ones
    > > are only updated once a second. Sometimes they only progress by one
    > > iteration, sometimes by a full round. Some are even updated once ever
    > > 2 seconds, because if I drag an xterm above them and quickly remove
    > > it, the xterm leaves a trace there for up to 2 seconds.
    > >
    > > Also, only one of my 2 CPUs is used. I see the rq vary between 1 and
    > > 5, with a permanent 50% idle... :
    > >
    > > procs memory swap io system cpu
    > > r b w swpd free buff cache si so bi bo in cs us sy id
    > > 1 0 0 0 874400 7864 90436 0 0 0 0 279 2204 50 0 50
    > > 3 0 0 0 874408 7864 90436 0 0 0 0 273 2122 50 1 50
    > > 1 0 0 0 874408 7864 90436 0 0 0 0 253 1660 49 1 50
    > > 3 0 0 0 874408 7864 90436 0 0 0 0 252 1977 50 0 50
    > > 2 0 0 0 874408 7864 90436 0 0 0 0 253 2274 49 1 50
    > > 3 0 0 0 874408 7864 90436 0 0 0 0 252 1846 49 1 50
    > > 1 0 0 0 874408 7864 90436 0 0 0 0 339 1782 49 1 50
    > >
    > > I have no idea about what version brought that unexpected behaviour,
    > > but it's clearly something which needs to be tracked down.
    >
    > hm, the two problems might be related. Could you try v17 perhaps? In v18
    > i have 'unified' all the sched.c's between the various kernel releases,
    > maybe that brought in something unexpected on 2.6.20.14. (perhaps try
    > v2.6.21.5 based cfs too?)

    Well, forget this, I'm nuts. I'm sorry, but I did not set any of the -R
    and -S parameter on ocbench, which means that all the processes ran at
    full speed and did not sleep. The load distribution was not fair, but
    since they put a lot of stress on the X server, I think it might be one
    of the reasons for the unfairness. I got the same behaviour with -v17,
    -v9 and even 2.4 ! It told me something was wrong on my side ;-)

    I've retried with 50%/50% run/sleep, and it now works like a charm. It's
    perfectly smooth with both small and long run/sleep times (between 1 and 100
    ms). I think that with X saturated, it might explain why I only had one CPU
    running at 100% !

    Next time, I'll try to take a bit more time for such a test.

    > could you send me the file the cfs-debug-info.sh script produced. You
    > can pick the script up from:
    >
    > http://people.redhat.com/mingo/cfs-scheduler/tools/cfs-debug-info.sh

    OK I got it, but I've not run it since the problem was between the keyboard
    and the chair. If you want an output anyway, I can give it a run.

    Sorry again for the wrong alert.

    regards,
    willy

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