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SubjectRe: [ANNOUNCE/RFC] Really Fair Scheduler

* Daniel Walker <dwalker@mvista.com> wrote:

> The the patch is near the end of this email.. The most notable thing
> about the rediff is the line count,
>
> 4 files changed, 323 insertions(+), 729 deletions(-)
>
> That's impressive (assuming my rediff is correct). [...]

Yeah, at first glance i liked that too, then i looked into the diff and
noticed that a good chunk of the removal "win" comes from the removal of
~35 comment blocks while adding new code that has no comments at all
(!).

And if you look at the resulting code size/complexity, it actually
increases with Roman's patch (UP, nodebug, x86):

text data bss dec hex filename
13420 228 1204 14852 3a04 sched.o.rc5
13554 228 1228 15010 3aa2 sched.o.rc5-roman

Although it _should_ have been a net code size win, because if you look
at the diff you'll see that other useful things were removed as well:
sleeper fairness, CPU time distribution smarts, tunings, scheduler
instrumentation code, etc.

> I also ran hackbench (in a haphazard way) a few times on it vs. CFS in
> my tree, and RFS was faster to some degree (it varied)..

here are some actual numbers for "hackbench 50" on -rc5, 10 consecutive
runs fresh after bootup, Core2Duo, UP:

-rc5(cfs) -rc5+rfs
-------------------------------
Time: 3.905 Time: 4.259
Time: 3.962 Time: 4.190
Time: 3.981 Time: 4.241
Time: 3.986 Time: 3.937
Time: 3.984 Time: 4.120
Time: 4.001 Time: 4.013
Time: 3.980 Time: 4.248
Time: 3.983 Time: 3.961
Time: 3.989 Time: 4.345
Time: 3.981 Time: 4.294
-------------------------------
Avg: 3.975 Avg: 4.160 (+4.6%)
Fluct: 0.138 Fluct: 1.671
so unmodified CFS is 4.6% faster on this box than with Roman's patch and
it's also more consistent/stable (10 times lower fluctuations).

At lower hackbench levels (hackbench 10) the numbers are closer - that
could be what you saw.

But, this measurement too is apples to oranges, given the amount of
useful code the patch removes - fact is that you can always speed up the
scheduler by removing stuff, just run hackbench as SCHED_FIFO (via "chrt
-f 90 ./hackbench 50") to see what a minimal scheduler can do.

It would be far more reviewable and objectively judgeable on an item by
item basis if Roman posted the finegrained patches i asked for. (which
patch series should be sorted in order of intrusiveness - i.e. leaving
the harder changes to the end of the series.)

Ingo
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