Scheduler in Various Docs

Jeremy Chadwick koitsu at
Sun Jan 20 11:13:16 PST 2008

On Sun, Jan 20, 2008 at 07:40:07PM +0100, TooMany Secrets wrote:
> On 1/20/08, Stephen Montgomery-Smith <stephen at> wrote:
> > Jason C. Wells wrote:
> > > The comments regarding SCHED_ULE and SCHED_4BSD are inconsistent with
> > > information found in the email archives.  LINT says ULE is experimental.
> > >     The handbook doesn't mention ULE at all. The archives say ULE is the
> > > new recommended scheduler.
> > >
> > > If ULE is in fact the current recommendation, then a few docs need to be
> > > updated.
> >
> > To add to Jason's point - why does GENERIC still default to SCHED_4BSD?
> >   Are there plans to change this before 7.0 is truly released?
> Excuse me for my bad english...
> This question was mentioned two or three months ago. The answer was
> that in 7.1, after the ULE will be tested in 7.0, it will be the
> defacto scheduler in FreeBSD. First, the scheduler need the best
> benchark in the world; a few thousand users testing in real-life
> situations on a daily basis.

This is correct.  There was a very large discussion on freebsd-current
(which would've been discussing 7.x at that point) about what scheduler
should be the default for RELENG_7 (4BSD or the "new" ULE (a.k.a.
SMP2)).  It was ""voted"" (note the quotes) that SCHED_4BSD should
remain the default until 7.1 was released, since if there turned out
to be a gigantic bug in the new scheduler, we wouldn't want people to
get bit by it (thus harming the stability reputation of -RELEASE and
-STABLE).  The 4BSD scheduler is still considered stable and has a
track record to prove it.

In a way, SCHED_ULE on 7.x is still considered "experimental" in the
sense that it needs lots of people testing it.  So far all the results
have been positive (unlike SCHED_ULE on 6.x and 5.x, which were very
broken -- hence the rewrite!).

If the OP wants to read the thread/discussion (it's long), I can dig up
a URL to it in the archives.

| Jeremy Chadwick                                    jdc at |
| Parodius Networking                  |
| UNIX Systems Administrator                      Mountain View, CA, USA |
| Making life hard for others since 1977.                  PGP: 4BD6C0CB |

More information about the freebsd-stable mailing list