Scheduler in Various Docs

Stephen Montgomery-Smith stephen at
Sun Jan 20 11:17:33 PST 2008

Jeremy Chadwick wrote:
> 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.

Thanks.  You both answered my question admirably.

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