Hi all,

Since the previous RFC v2, I've reimplemented smp-cache object based on
Daniel's comment (thanks Daniel!), which is both flexible to support
current cache topology requirements and extensible.

So, I officially convert the RFC to PATCH.

Background on smp cache topology can be found in the previous RFC v2
cover letter:

https://lore.kernel.org/qemu-devel/20240530101539.768484-1-zhao1.liu@intel.com/

The following content focuses on this series implementation of the
smp-cache object.


About smp-cache
===============

In fact, the smp-cache object introduced in this series is a bit
different from Daniel's original suggestion. Instead of being integrated
into -smp, it is created explicitly via -object, and the smp-cache
property is added to -machine to link to this object.

An example is as follows:

-object '{"qom-type":"smp-cache","id":"cache0","caches":[{"name":"l1d","topo":"core"},{"name":"l1i","topo":"core"},{"name":"l2","topo":"module"},{"name":"l3","topo":"socket"}]}'
-machine smp-cache=cache0


Such the design change is based on the following 2 reasons:
 * Defining the cache with a JSON list is very extensible and can
   support more cache properties.

 * But -smp, as the sugar of machine property "smp", is based on keyval
   format, and doesn't support options with JSON format. Thus it's not
   possible to add a JSON format based option to -smp/-machine for now.

So, I decoupled the creation of the smp-cache object from the -machine
to make both -machine and -object happy!


Welcome your feedback!


Thanks and Best Regards,
Zhao
---
Changelog:

Main changes since RFC v2:
 * Dropped cpu-topology.h and cpu-topology.c since QAPI has the helper
   (CpuTopologyLevel_str) to convert enum to string. (Markus)
 * Fixed text format in machine.json (CpuTopologyLevel naming, 2 spaces
   between sentences). (Markus)
 * Added a new level "default" to de-compatibilize some arch-specific
   topo settings. (Daniel)
 * Moved CpuTopologyLevel to qapi/machine-common.json, at where the
   cache enumeration and smp-cache object would be added.
   - If smp-cache object is defined in qapi/machine.json, storage-daemon
     will complain about the qmp cmds in qapi/machine.json during
     compiling.
 * Referred to Daniel's suggestion to introduce cache JSON list, though
   as a standalone object since -smp/-machine can't support JSON.
 * Linked machine's smp_cache to smp-cache object instead of a builtin
   structure. This is to get around the fact that the keyval format of
   -machine can't support JSON.
 * Wrapped the cache topology level access into a helper.
 * Split as a separate commit to just include compatibility checking and
   topology checking.
 * Allow setting "default" topology level even though the cache
   isn't supported by machine. (Daniel)
 * Rewrote the document of smp-cache object.

Main changes since RFC v1:
 * Split CpuTopology renaimg out of this RFC.
 * Use QAPI to enumerate CPU topology levels.
 * Drop string_to_cpu_topo() since QAPI will help to parse the topo
   levels.
 * Set has_*_cache field in machine_get_smp(). (JeeHeng)
 * Use "*_cache=topo_level" as -smp example as the original "level"
   term for a cache has a totally different meaning. (Jonathan)
---
Zhao Liu (8):
  hw/core: Make CPU topology enumeration arch-agnostic
  qapi/qom: Introduce smp-cache object
  hw/core: Add smp cache topology for machine
  hw/core: Check smp cache topology support for machine
  i386/cpu: Support thread and module level cache topology
  i386/cpu: Update cache topology with machine's configuration
  i386/pc: Support cache topology in -machine for PC machine
  qemu-options: Add the description of smp-cache object

 MAINTAINERS                 |   2 +
 hw/core/machine-smp.c       |  86 ++++++++++++++++++++++++++++++
 hw/core/machine.c           |  22 ++++++++
 hw/core/meson.build         |   1 +
 hw/core/smp-cache.c         | 103 ++++++++++++++++++++++++++++++++++++
 hw/i386/pc.c                |   4 ++
 include/hw/boards.h         |  11 +++-
 include/hw/core/smp-cache.h |  27 ++++++++++
 include/hw/i386/topology.h  |  18 +------
 qapi/machine-common.json    |  97 ++++++++++++++++++++++++++++++++-
 qapi/qapi-schema.json       |   4 +-
 qapi/qom.json               |   3 ++
 qemu-options.hx             |  58 ++++++++++++++++++++
 target/i386/cpu.c           |  83 +++++++++++++++++++++--------
 target/i386/cpu.h           |   4 +-
 15 files changed, 478 insertions(+), 45 deletions(-)
 create mode 100644 hw/core/smp-cache.c
 create mode 100644 include/hw/core/smp-cache.h

-- 
2.34.1