[RFC PATCH v4 0/7] hw/arm/virt: Introduce cpu topology support

[Yanan Wang <wangyanan55@huawei.com>]

Hi,

This is v4 of the series [1] that I posted to introduce support for
generating cpu topology descriptions to guest. Comments are welcome!

Description:
Once the view of an accurate virtual cpu topology is provided to guest,
with a well-designed vCPU pinning to the pCPU we may get a huge benefit,
e.g., the scheduling performance improvement. See Dario Faggioli's
research and the related performance tests in [2] for reference. So here
we go, this patch series introduces cpu topology support for ARM platform.

In this series, instead of quietly enforcing the support for the latest
machine type, a new parameter "expose=on|off" in -smp command line is
introduced to leave QEMU users a choice to decide whether to enable the
feature or not. This will allow the feature to work on different machine
types and also ideally compat with already in-use -smp command lines.
Also we make much stricter requirement for the topology configuration
with "expose=on".

Furthermore, both cpu-map in DT and ACPI PPTT table are introduced to
present cpu topology to the guest. And an ARM-specific -smp parsing
function virt_smp_parse is introduced, which shares the same logic
with smp_parse() when "expose=off" and follow the stricter parsing
rule when "expose=on".

[1] https://patchwork.kernel.org/project/qemu-devel/cover/20210516102900.28036-1-wangyanan55@huawei.com/
[2] https://kvmforum2020.sched.com/event/eE1y/virtual-topology-for-virtual-machines-friend-or-foe-dario-faggioli-suse

Test results about exposure of topology:
After applying this patch series, launch an ACPI guest with virt-6.1 on an ARM server.

1) Enable the support:
With cmdline: -smp 96,sockets=2,cores=48,threads=1,expose=on
  or cmdline: -smp 96,maxcpus=96,sockets=2,cores=48,threads=1,expose=on
we get:
Architecture:        aarch64
Byte Order:          Little Endian
CPU(s):              96
On-line CPU(s) list: 0-95
Thread(s) per core:  1
Core(s) per socket:  48
Socket(s):           2
NUMA node(s):        1
Vendor ID:           0x48
Model:               0
Stepping:            0x1
BogoMIPS:            200.00
NUMA node0 CPU(s):   0-95

2) Disable the support:
With cmdline: -smp 96
  or cmdline: -smp 96,expose=off
we get:
Architecture:        aarch64
Byte Order:          Little Endian
CPU(s):              96
On-line CPU(s) list: 0-95
Thread(s) per core:  1
Core(s) per socket:  96
Socket(s):           1
NUMA node(s):        1
Vendor ID:           0x48
Model:               0
Stepping:            0x1
BogoMIPS:            200.00
NUMA node0 CPU(s):   0-95

---

Changelogs:

v3->v4:
- add new -smp parameter "expose=on|off" for users to enable/disable the feature
- add stricter -smp cmdline parsing rules on "expose=on" case
- move build_pptt to generic aml-build.c
- add default cluster node in the cpu-map
- rebase on top of latest upstream master
- v3: https://patchwork.kernel.org/project/qemu-devel/cover/20210516102900.28036-1-wangyanan55@huawei.com/

v2->v3:
- address comments from David, Philippe, and Andrew. Thanks!
- split some change into separate commits for ease of review
- adjust parsing rules of virt_smp_parse to be more strict
  (after discussion with Andrew)
- adjust author credit for the patches
- v2: https://patchwork.kernel.org/project/qemu-devel/cover/20210413080745.33004-1-wangyanan55@huawei.com/

v1->v2:
- Address Andrew Jones's comments
- Address Michael S. Tsirkin's comments
- v1: https://patchwork.kernel.org/project/qemu-devel/cover/20210225085627.2263-1-fangying1@huawei.com/

---

Andrew Jones (2):
  hw/arm/virt: Add cpu-map to device tree
  hw/acpi/aml-build: Generate PPTT table

Yanan Wang (5):
  vl: Add expose=on|off option support in -smp command line
  hw/arm/virt: Add separate -smp parsing function for ARM machines
  machine: disallow -smp expose=on for non-ARM machines
  device_tree: Add qemu_fdt_add_path
  hw/acpi/aml-build: Add Processor hierarchy node structure

 hw/acpi/aml-build.c          |  75 +++++++++++++++
 hw/arm/virt-acpi-build.c     |   8 +-
 hw/arm/virt.c                | 171 +++++++++++++++++++++++++++++++++--
 hw/core/machine.c            |   7 ++
 hw/i386/pc.c                 |   7 ++
 include/hw/acpi/aml-build.h  |   7 ++
 include/hw/boards.h          |   1 +
 include/sysemu/device_tree.h |   1 +
 qemu-options.hx              |  24 +++--
 softmmu/device_tree.c        |  44 ++++++++-
 softmmu/vl.c                 |   3 +
 11 files changed, 326 insertions(+), 22 deletions(-)

-- 
2.23.0