Re: Periodic rant about SCHED_ULE

From: Mark Millard <>
Date: Thu, 23 Mar 2023 20:45:41 UTC
Warner Losh <> wrote on
Date: Wed, 22 Mar 2023 22:57:08 UTC :

> On Wed, Mar 22, 2023 at 1:41 PM George Mitchell <>
> wrote:
> > service dnetc start
> > I am literally running "make buildworld" with no additional options.
> >
> >
> So what are the results for make buildworld -j $(sysctl -n hw.ncpu )?

Note: My experiments have been in this -j $(sysctl -n hw.ncpu )

> ULE scales much better, but when there's too little to do it can make poor
> choices.
> ULE is better locked and don't fall over on high core count systems like
> BSD does at moderate load.

(I'm presuming the above is not about the specifics
of the effectively different interpretations of the
likes of having extra "nice 20" activity by the two
schedulers for the examples related to the original
"rant", other than the -jN issue.)

Any idea on what scale "high core count systems" need to be
for what sort of "moderate load" to end up with signficant
differences? What sort of context(s) show ULE scaling much
better? On the 16 core ThreadRipper 1950X (32 hardware
threads) I've really only demonstrated the "nice 20"
distinction as significant between the schedulers so far.
(I do not have acccess to anything with more hardware threads.)

Note: I've not (yet?) been looking at having just a little
more than the number of hardware threads active (no nice

Mark Millard
marklmi at