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

[Vincent Guittot]

Hi Barry,

On Fri, 1 Oct 2021 at 12:32, Barry Song <21cnbao at gmail.com> wrote:
>
> Hi Vincent, Dietmar, Peter, Ingo,
> Do you have any comment on this first series which exposes cluster topology
> of ARM64 kunpeng 920 & x86 Jacobsville and supports load balance only for
> the 1st stage?
> I will be very grateful for your comments so that things can move forward in the
> right direction. I think Tim also looks forward to bringing up cluster
> support in
> Jacobsville.

This patchset makes sense to me and the addition of a new scheduling
level to better reflect the HW topology goes in the right direction.

>
> Best Regards
> Barry
>
> On Fri, Sep 24, 2021 at 8:51 PM Barry Song <21cnbao at gmail.com> wrote:
> >
> > From: Barry Song <song.bao.hua at hisilicon.com>
> >
> > ARM64 machines like kunpeng920 and x86 machines like Jacobsville have a
> > level of hardware topology in which some CPU cores, typically 4 cores,
> > share L3 tags or L2 cache.
> >
> > That means spreading those tasks between clusters will bring more memory
> > bandwidth and decrease cache contention. But packing tasks might help
> > decrease the latency of cache synchronization.
> >
> > We have three series to bring up cluster level scheduler in kernel.
> > This is the first series.
> >
> > 1st series(this one): make kernel aware of cluster, expose cluster to sysfs
> > ABI and add SCHED_CLUSTER which can make load balance between clusters to
> > benefit lots of workload.
> > Testing shows this can hugely boost the performance, for example, this
> > can increase 25.1% of SPECrate mcf on Jacobsville and 13.574% of mcf
> > on kunpeng920.
> >
> > 2nd series(wake_affine): modify the wake_affine and let kernel select CPUs
> > within cluster first before scanning the whole LLC so that we can benefit
> > from the lower latency of cache coherence within one single cluster. This
> > series is much more tricky. so we would like to send it after we build
> > the base of cluster by the 1st series. Prototype for 2nd series is here:
> > https://op-lists.linaro.org/pipermail/linaro-open-discussions/2021-June/000219.html
> >
> > 3rd series: a sysctl to permit users to enable or disable cluster scheduler
> > from Tim Chen. Prototype here:
> > Add run time sysctl to enable/disable cluster scheduling
> > https://op-lists.linaro.org/pipermail/linaro-open-discussions/2021-July/000258.html
> >
> > This series is resent and rebased on 5.15-rc2.
> >
> > -V1:
> >  differences with RFC v6
> >  * removed wake_affine path modifcation, which will be separately second series
> >  * cluster_id is gotten by detecting valid ID before falling back to use offset
> >  * lots of benchmark data from both x86 Jacobsville and ARM64 kunpeng920
> >
> > -RFC v6:
> > https://lore.kernel.org/lkml/20210420001844.9116-1-song.bao.hua@hisilicon.com/
> >
> > Barry Song (1):
> >   scheduler: Add cluster scheduler level in core and related Kconfig for
> >     ARM64
> >
> > Jonathan Cameron (1):
> >   topology: Represent clusters of CPUs within a die
> >
> > Tim Chen (1):
> >   scheduler: Add cluster scheduler level for x86
> >
> >  Documentation/ABI/stable/sysfs-devices-system-cpu | 15 +++++
> >  Documentation/admin-guide/cputopology.rst         | 12 ++--
> >  arch/arm64/Kconfig                                |  7 +++
> >  arch/arm64/kernel/topology.c                      |  2 +
> >  arch/x86/Kconfig                                  |  8 +++
> >  arch/x86/include/asm/smp.h                        |  7 +++
> >  arch/x86/include/asm/topology.h                   |  3 +
> >  arch/x86/kernel/cpu/cacheinfo.c                   |  1 +
> >  arch/x86/kernel/cpu/common.c                      |  3 +
> >  arch/x86/kernel/smpboot.c                         | 44 ++++++++++++++-
> >  drivers/acpi/pptt.c                               | 67 +++++++++++++++++++++++
> >  drivers/base/arch_topology.c                      | 14 +++++
> >  drivers/base/topology.c                           | 10 ++++
> >  include/linux/acpi.h                              |  5 ++
> >  include/linux/arch_topology.h                     |  5 ++
> >  include/linux/sched/topology.h                    |  7 +++
> >  include/linux/topology.h                          | 13 +++++
> >  kernel/sched/topology.c                           |  5 ++
> >  18 files changed, 223 insertions(+), 5 deletions(-)
> >
> > --
> > 1.8.3.1
> >