Re: [PATCH] Nick's scheduler policy v10

[Nick Piggin]

Martin J. Bligh wrote:

> > This is quite a big change from v8. Fixes a few bugs in child priority,
> > and adds a small lower bound on the amount of history that is kept. This
> > should improve "fork something" times hopefully, and stops new children
> > being able to fluctuate priority so wildly.
> >
> > Eliminates "timeslice backboost" and only uses "priority backboost". This
> > decreases scheduling latency quite nicely - I can only measure 130ms for
> > a very low priority task, with a make -j3 and wildly moving an xterm around
> > in front of a mozilla window.
> >
> > Makes a fairly fundamental change to how sleeping/running is accounted.
> > It now takes into account time on the runqueue. This hopefully will keep
> > priorities more stable under varying loads.
> >
> > Includes an upper bound on the amount of priority a task can get in one
> > sleep. Hopefully this catches freak long sleeps like a SIGSTOP or unexpected
> > swaps. This change breaks the priority calculation a little bit. I'm thinking
> > about how to fix it.
> >
> > Feedback welcome! Its against 0-test4, as usual.
>
> Oooh - much better.
>
> Kernbench: (make -j vmlinux, maximal tasks)
>                              Elapsed      System        User         CPU
>              2.6.0-test4       45.87      116.92      571.10     1499.00
>         2.6.0-test4-nick       49.37      131.31      611.15     1500.75
>       2.6.0-test4-nick7a       49.48      125.95      617.71     1502.00
>       2.6.0-test4-nick10       46.91      114.03      584.16     1489.25
>
> SDET 128  (see disclaimer)
>                           Throughput    Std. Dev
>              2.6.0-test4       100.0%         0.3%
>         2.6.0-test4-nick       102.9%         0.3%
>       2.6.0-test4-nick7a       105.1%         0.5%
>       2.6.0-test4-nick10       107.7%         0.2%

Nice.

> System time of kernbench is back to what it would be with virgin, or
> actually a little less. Elapsed time is still up a little bit, along
> with user time, but it's getting pretty close.
>
> Have you looked at Rick Lindsley's schedstat patches? I don't have a
> totally up-to-date version, but that might give us a better idea of
> what's going on wrt migrations, balancing, etc.

I haven't had a look, no. I will see.

> I'll try to get together a broader set of benchmarks and hammer on this
> some more ...

That would be cool. It seems to be rapidly becoming "acceptable" to
desktop users, so high end tuning needs to be next. But hopefully I
might not have to do much.


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