Re: Periodic rant about SCHED_ULE

From: Steve Kargl <sgk_at_troutmask.apl.washington.edu>
Date: Wed, 7 Jul 2021 14:49:19 -0700
On Wed, Jul 07, 2021 at 10:56:55PM +0200, Miroslav Lachman wrote:
> On 07/07/2021 20:18, Gary Jennejohn wrote:
> > On Wed, 7 Jul 2021 13:47:47 -0400
> > George Mitchell <george+freebsd_at_m5p.com> 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.
> 

I made those measurements more than a decade ago, and 
reported my findings in either freebsd-hackers or 
freebsd-current mailing list.

Write a classic boss-worker MPI numerical simulation, where the
workers are compute bound.  Start the MPI simulation requesting
NCPU+1 images with NCPU being the number of available cpus.
Each worker will be assigned to a cpu.  Then this leads to a
worker and the boss image sharing a cpu.  Due to cpu affinity,
these two then ping-pong on that cpu.

I haven't repeated these measurement in a long time.

-- 
Steve
Received on Wed Jul 07 2021 - 21:49:19 UTC

Original text of this message