huge nanosleep variance on 11-stable

[George Mitchell]

On 11/01/16 23:45, Kevin Oberman wrote:
> On Tue, Nov 1, 2016 at 2:36 PM, Jason Harmening <jason.harmening at gmail.com>
> wrote:
> 
>> Sorry, that should be ~*30ms* to get 30fps, though the variance is still
>> up to 500ms for me either way.
>>
>> On 11/01/16 14:29, Jason Harmening wrote:
>>> repro code is at http://pastebin.com/B68N4AFY if anyone's interested.
>>>
>>> On 11/01/16 13:58, Jason Harmening wrote:
>>>> Hi everyone,
>>>>
>>>> I recently upgraded my main amd64 server from 10.3-stable (r302011) to
>>>> 11.0-stable (r308099).  It went smoothly except for one big issue:
>>>> certain applications (but not the system as a whole) respond very
>>>> sluggishly, and video playback of any kind is extremely choppy.
>>>>
>>>> [...]
> I eliminated the annoyance by change scheduler from ULE to 4BSD. That was
> it, but I have not seen the issue since. I'd be very interested in whether
> the scheduler is somehow impacting timing functions or it's s different
> issue. I've felt that there was something off in ULE for some time, but it
> was not until these annoying hiccups convinced me to try going back to
> 4BSD.
> 
> Tip o' the hat to Doug B. for his suggestions that ULE may have issues that
> impacted interactivity.
> [...]

Not to beat a dead horse, but I've been a non-fan of SCHED_ULE since
it was first introduced, and I don't like it even today.  I run the
distributed.net client on my machines, but even without that, ULE
screws interactive behavior.  With distributed.net running and ULE,
a make buildworld/make buildkernel takes 10 2/3 hours on 10.3-RELEASE
on a 6-CPU machine versus 2 1/2 hours on the same machine with 4BSD
and distributed.net running.  I'm told that SCHED_ULE is the greatest
thing since sliced bread for some compute load or other (details are
scarce), but I (fortunately) don't often have to run heavy server
type loads; and for everyday use (even without distributed.net
running), SCHED_4BSD is my choice by far.  It's too bad I can't run
freebsd_update with it, though.

I promise to shut up about this now.                       -- George