NFS client perf. degradation when SCHED_ULE is used (was when SMP enabled)

[Rick Macklem]

To briefly summarize the previous post related to perf. degradation when running a
recent kernel...
- kernel build running 1yr old kernel took     100minutes
- same kernel build running recent kernel     148minutes
(ie. Almost a 50% degradation.)
As noted in the last post, I got rid of most of the degradation by disabling SMP.

- same kernel build running recent kernel with SCHED_4BSD   104minutes

I have now found I can get rid of almost all of the degradation by building the
recent kernel with
options SCHED_4BSD
instead of
options SCHED_ULE

The 1yr old kernel was built with SCHED_ULE, so the degradation is some change
to the kernel since Apr. 12, 2016 that affects SCHED_ULE but not SCHED_4BSD.

Any ideas?

Since GENERIC uses SCHED_ULE, it would be nice to see good perf. with that option.
However, recommending "options SCHED_4BSD" is nicer than recommending disabling
SMP;-)

rick
ps: I tried the 1yr old net driver in the recent kernel and it had no effect on perf.