Re: [PATCH 1/2] sched: Add default dynamic preempt mode Kconfig

From: Frederic Weisbecker
Date: Wed Jun 09 2021 - 07:27:55 EST


On Tue, Jun 08, 2021 at 04:04:47PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 08, 2021 at 03:55:09PM +0200, Peter Zijlstra wrote:
> > Urgh, would something like this work?
> >
> > ---
> > kernel/Kconfig.preempt | 64 ++++++++++++++++++++++++++++++++++++++++----------
> > 1 file changed, 51 insertions(+), 13 deletions(-)
> >
> > diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
> > index bd7c4147b9a8..43c68a806e4e 100644
> > --- a/kernel/Kconfig.preempt
> > +++ b/kernel/Kconfig.preempt
> > @@ -1,11 +1,25 @@
> > # SPDX-License-Identifier: GPL-2.0-only
> >
> > +config PREEMPT_COUNT
> > + bool
> > +
> > +config PREEMPTION
> > + bool
> > + select PREEMPT_COUNT
> > +
> > +config PREEMPT_DYNAMIC_OPTION
> > + bool
> > + help
> > + Symbol that gates availablility of PREEMPT_DYNAMIC, selected
> > + by preemption models that can be dynamically selected.
> > +
> > choice
> > prompt "Preemption Model"
> > + default PREEMPT_TYPE_NONE
> >
> > +config PREEMPT_TYPE_NONE
> > bool "No Forced Preemption (Server)"
> > + select PREEMPT_DYNAMIC_OPTION if HAVE_PREEMPT_DYNAMIC
> > help
> > This is the traditional Linux preemption model, geared towards
> > throughput. It will still provide good latencies most of the
> > @@ -17,9 +31,10 @@ config PREEMPT_NONE
> > raw processing power of the kernel, irrespective of scheduling
> > latencies.
> >
> > +config PREEMPT_TYPE_VOLUNTARY
> > bool "Voluntary Kernel Preemption (Desktop)"
> > depends on !ARCH_NO_PREEMPT
> > + select PREEMPT_DYNAMIC_OPTION if HAVE_PREEMPT_DYNAMIC
> > help
> > This option reduces the latency of the kernel by adding more
> > "explicit preemption points" to the kernel code. These new
> > @@ -35,12 +50,10 @@ config PREEMPT_VOLUNTARY
> >
> > Select this if you are building a kernel for a desktop system.
> >
> > -config PREEMPT
> > +config PREEMPT_TYPE_FULL
> > bool "Preemptible Kernel (Low-Latency Desktop)"
> > depends on !ARCH_NO_PREEMPT
> > + select PREEMPT_DYNAMIC_OPTION if HAVE_PREEMPT_DYNAMIC
> > help
> > This option reduces the latency of the kernel by making
> > all kernel code (that is not executing in a critical section)
> > @@ -75,15 +88,24 @@ config PREEMPT_RT
> >
> > endchoice
> >
> > +# default model for PREEMPT_DYNAMIC
> >
> > +config PREEMPT_DYNAMIC_NONE
> > + bool
> >
> > +config PREEMPT_DYNAMIC_VOLUNTARY
> > + bool
> > +
> > +config PREEMPT_DYNAMIC_FULL
> > bool
> > +
> > +config PREEMPT_DYNAMIC
> > + bool "Dynamic Preemption Mode"
> > + depends on PREEMPT_DYNAMIC_OPTION
> > + select PREEMPT
> > + select PREEMPT_DYNAMIC_NONE if PREEMPT_TYPE_NONE
> > + select PREEMPT_DYNAMIC_VOLUNTARY if PREEMPT_TYPE_VOLUNTARY
> > + select PREEMPT_DYNAMIC_FULL if PREEMPT_TYPE_FULL
>
> Arguably PREEMPT_DYNAMIC_{NONE,VOLUNTARY,FULL} are superfluous and the
> default selection can use PREEMPT_TYPE_*.

Right, I'll try that.

Thanks.