Re: Periodic rant about SCHED_ULE

From: Miroslav Lachman <>
Date: Wed, 07 Jul 2021 20:56:55 UTC
On 07/07/2021 20:18, Gary Jennejohn wrote:
> On Wed, 7 Jul 2021 13:47:47 -0400
> George Mitchell <> wrote:


>> I've been ranting about this for years now, and I've had my say -- but
>> no one has ever answered my question about what workload SCHED_ULE is
>> best for, though numerous people have claimed that it's better than
>> SCHED_4BSD for -- some rumored workload or other.          -- George
> IIRC there was talk about making the scheduler loadable in the early
> days.  But that was years ago and I may be misrembering.
> I have a Ryzen 5 1600 with 6 cores, so older tech and "only" 3200MHz.
> I can do a clean buildworld on FreeBSD-14 using only 10 of the 12 SMTs
> in about 40 minutes using SCHED_4BSD.  While still browsing the
> interwebs or watching a film etc.  with no noticeable lags in
> performance.
> So, for my normal desktop usage SCHED_4BSD is the only way to go.

I had some performance problems with VirtualBox as hypervisor on 
somewhat older Intel Xeon with 4 cores 8 threads. So I tested 4BSD and 
ULE -  SCHED_4BSD had slightly better results than SCHED_ULE.
I am also curious why ULE is the default. Where are some real world 
performance results for comparing the two FreeBSD schedulers.

Kind regards
Miroslav Lachman