ULE vs. 4BSD in RELENG_7

[Josh Carroll]

> Josh, thanks for your help so far.  This has been very useful.

You're welcome, glad to help! Thanks for the effort and the patch.

> Any testing you can run this through is appreciated.  Anyone else lurking
> in this thread who would like to is also welcome to report back findings.

Here are a few benchmarks comparing ULE and the patched ULE. I
experimented in changing the slice_min value from 2 to 4, in case that
might be useful info for you. Hopefully that helps a bit, but if not
it's just a few minutes of CPU time wasted :)

Sysbench results:
# threads    slice=7     slice=13     slice_min=4      slice_min=2
4                2265.67    2250.36      2261.71            2297.08
8                2300.25    2310.02      2306.79            2313.61
12              2269.54    2304.04      2296.54            2279.73
16              2249.26    2252.04      2260.53            2245.76

It looks like with the default minimum (2), the performance for systat
is better with 4 and 8 threads (on a 4 core system), but worse for 12
and 16 threads.

Here are the results for ffmpeg (-threads 8):

slice=7      slice=13       slice_min=4         slice_min=2
1:37.00      1:39.09         1:38.12                1:38.06

The patch definitely improves things there, though not quite as good
as using a slice value of 7. But it does improve things. So it
slightly improves things for ffmpeg and also slightly increases the
performance of sysbench/MySQL (with 8 threads).

I also ran through buildworld for both slice_min of 2 and 4, and here
are the results, again with ULE as a base line:

slice=7      slice=13       slice_min=4         slice_min=2
13:40.56    13:44.28       13:46.64              13:45.80

So buildworld performance is about the same as with the default ULE
and default slice value.

Thanks,
Josh