kern.sched.quantum: Creepy, sadistic scheduler

Freddie Cash fjwcash at gmail.com
Tue Apr 17 16:05:53 UTC 2018


On Tue, Apr 17, 2018 at 8:49 AM, Kevin Oberman <rkoberman at gmail.com> wrote:

> On Mon, Apr 16, 2018 at 11:56 PM, Eivind Nicolay Evensen <
> eivinde at terraplane.org> wrote:
>
> > On Wed, Apr 04, 2018 at 09:32:58AM -0400, George Mitchell wrote:
> > > On 04/04/18 06:39, Alban Hertroys wrote:
> > > > [...]
> > > > That said, SCHED_ULE (the default scheduler for quite a while now)
> was
> > designed with multi-CPU configurations in mind and there are claims that
> > SCHED_4BSD works better for single-CPU configurations. You may give that
> a
> > try, if you're not already on SCHED_4BSD.
> > > > [...]
> > >
> > > A small, disgruntled community of FreeBSD users who have never seen
> > > proof that SCHED_ULE is better than SCHED_4BSD in any environment
> > > continue to regularly recompile with SCHED_4BSD.  I dread the day when
> > > that becomes impossible, but at least it isn't here yet.      -- George
> >
> > Indeed 4bsd is better in my case aswell. While for some unknown to me
> > reason ule performed a bit better in the 10.x series than before, in 11.x
> > it again is in my case not usable.
> >
> > Mouse freezes for around half a second with even frequency by just moving
> > it around in x11. Using 4bsd instead makes the problem go away.
> > I'm actually very happy that ule became worse again because going
> > back to 4bsd yet again also gave improved performance from other
> > dreadfully slow but (to me) still useful programs, like darktable.
> >
> > With 4bsd, when adjusting shadows and highlights it is possible to see
> > what I do when moving sliders. With ule it has never been better than
> waiting
> > 10-20-30 seconds to see where it was able to read a slider position
> > and update display, when working on images around 10500x10500 greyscale.
> >
> > It's not single cpu/single core either:
> > CPU: AMD FX(tm)-6300 Six-Core Processor              (3817.45-MHz
> K8-class
> > CPU)
>
> My experience has long been that 4BSD works far better for interactive, X
> based systems than ULE. Even on 10 I saw long, annoying pauses with ULE and
> I don't se those with 4BSD. I'd really like to see it better known that
> this is often the case. BTW, my system is 2 core/4 thread Sandybridge.
>>

​The following has been suggested multiple times over the years on various
mailing lists as the "solution" to making ULE work well for interactive
tasks like running X-based desktops (in /etc/sysctl.conf):​

# Tune for desktop usage
kern.sched.preempt_thresh=224

​Works quite nicely on a 4-core AMD Phenom-II X4 960T Processor
(3010.09-MHz K8-class CPU) running KDE4 using an Nvidia 210 GPU.

-- 
Freddie Cash
fjwcash at gmail.com


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