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Re: [PATCH v4 00/10] ARM virt: Introduce CPU clusters topology support

From: wangyanan (Y)
Subject: Re: [PATCH v4 00/10] ARM virt: Introduce CPU clusters topology support
Date: Thu, 16 Dec 2021 11:22:50 +0800
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0


On 2021/11/21 20:24, Yanan Wang wrote:

This series introduces the new CPU clusters topology parameter
and enable the support for it on ARM virt machines.

Background and descriptions:
The new Cluster-Aware Scheduling support has landed in Linux 5.16,
which has been proved to benefit the scheduling performance (e.g.
load balance and wake_affine strategy) on both x86_64 and AArch64.
We can see Kernel PR [1] and the latest patch set [2] for reference.

So now in Linux 5.16 we have four-level arch-neutral CPU topology
definition like below and a new scheduler level for clusters.
struct cpu_topology {
     int thread_id;
     int core_id;
     int cluster_id;
     int package_id;
     int llc_id;
     cpumask_t thread_sibling;
     cpumask_t core_sibling;
     cpumask_t cluster_sibling;
     cpumask_t llc_sibling;

A cluster generally means a group of CPU cores which share L2 cache
or other mid-level resources, and it is the shared resources that
is used to improve scheduler's behavior. From the point of view of
the size range, it's between CPU die and CPU core. For example, on
some ARM64 Kunpeng servers, we have 6 clusters in each NUMA node,
and 4 CPU cores in each cluster. The 4 CPU cores share a separate
L2 cache and a L3 cache tag, which brings cache affinity advantage.

[2] https://lkml.org/lkml/2021/9/24/178

In virtualization, on the Hosts which have pClusters, if we can
design a vCPU topology with cluster level for guest kernel and
have a dedicated vCPU pinning. A Cluster-Aware Guest kernel can
also make use of the cache affinity of CPU clusters to gain
similar scheduling performance.

This series consists of two parts:
The first part (patch 1-3):
Implement infrastructure for CPU cluster level topology support,
including the SMP documentation, configuration and parsing.

The second part (part 4-10):
Enable CPU cluster support on ARM virt machines, so that users
can specify a 4-level CPU hierarchy sockets/clusters/cores/threads.
And the 4-level topology will be described to guest kernel through
ACPI PPTT and DT cpu-map.

- Significant change from v3 to v4, since the whole series is reworked
   based on latest QEMU SMP frame.
- v3: 

Yanan Wang (10):
   qemu-options: Improve readability of SMP related Docs
   hw/core/machine: Introduce CPU cluster topology support
   hw/core/machine: Wrap target specific parameters together
   hw/arm/virt: Support clusters on ARM virt machines
   hw/arm/virt: Support cluster level in DT cpu-map
   hw/acpi/aml-build: Improve scalability of PPTT generation
   hw/arm/virt-acpi-build: Make an ARM specific PPTT generator
   tests/acpi/bios-tables-test: Allow changes to virt/PPTT file
   hw/acpi/virt-acpi-build: Support cluster level in PPTT generation
   tests/acpi/bios-table-test: Update expected virt/PPTT file

  hw/acpi/aml-build.c         |  66 ++------------------------
  hw/arm/virt-acpi-build.c    |  92 +++++++++++++++++++++++++++++++++++-
  hw/arm/virt.c               |  16 ++++---
  hw/core/machine-smp.c       |  29 +++++++++---
  hw/core/machine.c           |   3 ++
  include/hw/acpi/aml-build.h |   5 +-
  include/hw/boards.h         |   6 ++-
  qapi/machine.json           |   5 +-
  qemu-options.hx             |  91 +++++++++++++++++++++++++++--------
  softmmu/vl.c                |   3 ++
  tests/data/acpi/virt/PPTT   | Bin 76 -> 96 bytes
  11 files changed, 214 insertions(+), 102 deletions(-)



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