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

[Barry Song]

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.

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
>