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

[Barry Song]

From: Barry Song <song.bao.hua@xxxxxxxxxxxxx>

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 among 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(packing path): 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 the communication within one single cluster.
this series is much more tricky. so we would like to send it after the 1st
series settles down. Prototype 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 rebased on Greg's driver-core-next with the update in topology
sysfs ABI.

-V1:
 differences with RFC v6 
 * rebased on top of the latest update in topology sysfs ABI of Greg's
   driver-core-next
 * removed wake_affine path modifcation, which will be separately b2nd 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@xxxxxxxxxxxxx/

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

 .../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(-)

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2.25.1