[PATCH for-6.2 v5 0/5] hw/arm/virt: Introduce cpu topology support

[Yanan Wang <wangyanan55@huawei.com>]

Hi,

This is a new version (v5) of the series [1] that I posted to introduce
support for generating cpu topology descriptions to virt machine guest.

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.

This patch series introduces cpu topology support for ARM platform.
Both cpu-map in DT and ACPI PPTT table are introduced to store the
topology information. And we only describe the topology information
to 6.2 and newer virt machines, considering compatibility.

[1] https://lore.kernel.org/qemu-devel/20210622093413.13360-1-wangyanan55@huawei.com/
[2] https://kvmforum2020.sched.com/event/eE1y/virtual-topology-for-virtual-machines
-friend-or-foe-dario-faggioli-suse

Some tests:
1) -smp 16,sockets=2,cores=4,threads=2,maxcpus=16
lscpu:
Architecture:        aarch64
Byte Order:          Little Endian
CPU(s):              16
On-line CPU(s) list: 0-15
Thread(s) per core:  2
Core(s) per socket:  4
Socket(s):           2
NUMA node(s):        1
Vendor ID:           ARM
Model:               2
Model name:          Cortex-A72
Stepping:            r0p2
BogoMIPS:            100.00
NUMA node0 CPU(s):   0-15

cat /sys/devices/system/cpu/present  -->  0-15
cat /sys/devices/system/cpu/possible -->  0-15

2) -smp 8,sockets=2,cores=4,threads=2,maxcpus=16
lscpu:
Architecture:        aarch64
Byte Order:          Little Endian
CPU(s):              8
On-line CPU(s) list: 0-7
Thread(s) per core:  2
Core(s) per socket:  4
Socket(s):           1
NUMA node(s):        1
Vendor ID:           ARM
Model:               2
Model name:          Cortex-A72
Stepping:            r0p2
BogoMIPS:            100.00
NUMA node0 CPU(s):   0-7

cat /sys/devices/system/cpu/present  -->  0-7
cat /sys/devices/system/cpu/possible -->  0-7

---

Changelogs:

v4->v5:
- drop the added -smp "expose=on|off" parameter and only describe topology
  for 6.2 and newer machines
- rebased the code on patch series [3] which has introduced some fix and
  improvement for smp parsing
- [3]: https://lore.kernel.org/qemu-devel/20210803080527.156556-1-wangyanan55@huawei.com/

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://lore.kernel.org/qemu-devel/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

v1->v2:
- Address Andrew Jones's comments
- Address Michael S. Tsirkin's comments

---

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

Yanan Wang (3):
  hw/arm/virt: Only describe cpu topology to guest since virt 6.2
  device_tree: Add qemu_fdt_add_path
  hw/acpi/aml-build: Add Processor hierarchy node structure

 hw/acpi/aml-build.c          | 76 ++++++++++++++++++++++++++++++++++++
 hw/arm/virt-acpi-build.c     |  8 +++-
 hw/arm/virt.c                | 62 ++++++++++++++++++++++++-----
 include/hw/acpi/aml-build.h  |  7 ++++
 include/hw/arm/virt.h        |  4 +-
 include/sysemu/device_tree.h |  1 +
 softmmu/device_tree.c        | 44 ++++++++++++++++++++-
 7 files changed, 188 insertions(+), 14 deletions(-)

-- 
2.19.1