Re: Periodic rant about SCHED_ULE

From: Gary Jennejohn <gljennjohn_at_gmail.com>
Date: Thu, 8 Jul 2021 08:41:23 +0200
On Wed, 7 Jul 2021 14:49:19 -0700
Steve Kargl <sgk_at_troutmask.apl.washington.edu> wrote:

> 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.
> 

I feel that I have to add that the 40 minute buildworld isn't due to
SCHED_4BSD alone, but that I have many features which I don't need
disabled in src.conf.  I'm pretty sure that a buildworld with every
feature enabled would take a lot longer on my system.

-- 
Gary Jennejohn
Received on Thu Jul 08 2021 - 06:41:23 UTC

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