Re: [PATCH RESEND 0/3] Represent cluster topology and enable load balance between clusters

[Barry Song]

On Tue, Oct 5, 2021 at 9:05 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Sat, Oct 02, 2021 at 08:09:58PM +1300, Barry Song wrote:
>
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index 7e4651a1aaf4..86821e83b935 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -993,8 +993,13 @@ config SCHED_CLUSTER
> >         bool "Cluster scheduler support"
> >         help
> >           Cluster scheduler support improves the CPU scheduler's decision
> > +         making when dealing with machines that have clusters of CPUs.
> > +         Cluster usually means a couple of CPUs which are placed closely
> > +         by sharing mid-level caches, last-level cache tags or internal
> > +         busses. For example, on Hisilicon Kunpeng920, each 4 CPUs share
> > +         LLC cache tags. This feature isn't a universal win because it
> > +         can bring a cost of slightly increased overhead in some places.
> > +         If unsure say N here.
> >
> >  config SCHED_SMT
> >         bool "SMT scheduler support"
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index bd27b1cdac34..940eb1fe0abb 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -1002,12 +1002,17 @@ config NR_CPUS
> >           to the kernel image.
> >
> >  config SCHED_CLUSTER
> > +       def_bool y
> > +       prompt "Cluster scheduler support"
> >         help
> >          Cluster scheduler support improves the CPU scheduler's decision
> > +        making when dealing with machines that have clusters of CPUs.
> > +        Cluster usually means a couple of CPUs which are placed closely
> > +        by sharing mid-level caches, last-level cache tags or internal
> > +        busses. For example, on x86 Jacobsville, each 4 CPUs share one
> > +        L2 cache.
>
>                         This feature isn't a universal win because it can bring
> > +        a cost of slightly increased overhead in some places. If unsure
> > +        say N here.
>
> That is a really odd addition to a default-y feature.
>
> How about I make both:
>
>         help
>           Cluster scheduler support improves the CPU scheduler's decision
>           making when dealing with machines that have clusters of CPUs.
>           Cluster usually means a couple of CPUs which are placed closely
>           by sharing mid-level caches, last-level cache tags or internal
>           busses.

looks good to me. thanks!

barry