Re: [PATCH v2 0/7] Introduce SMP Cache Topology

["Michael S. Tsirkin" <mst@redhat.com>]

On Sun, Sep 08, 2024 at 08:59:13PM +0800, Zhao Liu wrote:
> Hi all,
> 
> Compared with previous Patch v1 [1], I've put the cache properties list
> into -machine, this is to meet current needs and also remain compatible
> with my future topology support (more discussion details, pls refer [2]).
> 
> This series is based on the commit 1581a0bc928d ("Merge tag 'pull-ufs-
> 20240906' of https://gitlab.com/jeuk20.kim/qemu into staging ufs
> queue").


Needs review from QOM maintainers.

> Background
> ==========
> 
> The x86 and ARM (RISCV) need to allow user to configure cache properties
> (current only topology):
>  * For x86, the default cache topology model (of max/host CPU) does not
>    always match the Host's real physical cache topology. Performance can
>    increase when the configured virtual topology is closer to the
>    physical topology than a default topology would be.
>  * For ARM, QEMU can't get the cache topology information from the CPU
>    registers, then user configuration is necessary. Additionally, the
>    cache information is also needed for MPAM emulation (for TCG) to
>    build the right PPTT. (Originally from Jonathan)
> 
> 
> About smp-cache
> ===============
> 
> In this version, smp-cache is implemented as a array integrated in
> -machine. Though -machine currently can't support JSON format, this is
> the one of the directions of future.
> 
> An example is as follows:
> 
> smp_cache=smp-cache.0.cache=l1i,smp-cache.0.topology=core,smp-cache.1.cache=l1d,smp-cache.1.topology=core,smp-cache.2.cache=l2,smp-cache.2.topology=module,smp-cache.3.cache=l3,smp-cache.3.topology=die
> 
> "cache" specifies the cache that the properties will be applied on. This
> field is the combination of cache level and cache type. Now it supports
> "l1d" (L1 data cache), "l1i" (L1 instruction cache), "l2" (L2 unified
> cache) and "l3" (L3 unified cache).
> 
> "topology" field accepts CPU topology levels including "thread", "core",
> "module", "cluster", "die", "socket", "book", "drawer" and a special
> value "default".
> 
> The "default" is introduced to make it easier for libvirt to set a
> default parameter value without having to care about the specific
> machine (because currently there is no proper way for machine to
> expose supported topology levels and caches).
> 
> If "default" is set, then the cache topology will follow the
> architecture's default cache topology model. If other CPU topology level
> is set, the cache will be shared at corresponding CPU topology level.
> 
> 
> Welcome your comment!
> 
> 
> [1]: Patch v1: https://lore.kernel.org/qemu-devel/20240704031603.1744546-1-zhao1.liu@intel.com/
> [2]: API disscussion: https://lore.kernel.org/qemu-devel/8734ndj33j.fsf@pond.sub.org/
> 
> Thanks and Best Regards,
> Zhao
> ---
> Changelog:
> 
> Main changes since Patch v1:
>  * Dropped handwriten smp-cache object and integrated cache properties
>    list into MachineState and used -machine to configure SMP cache
>    properties. (Markus)
>  * Dropped prefix of CpuTopologyLevel enumeration. (Markus)
>  * Rename CPU_TOPO_LEVEL_* to CPU_TOPOLOGY_LEVEL_* to match the QAPI's
>    generated code. (Markus)
>  * Renamed SMPCacheProperty/SMPCacheProperties (QAPI structures) to
>    SmpCacheProperties/SmpCachePropertiesWrapper. (Markus)
>  * Renamed SMPCacheName (QAPI structure) to SmpCacheLevelAndType and
>    dropped prefix. (Markus)
>  * Renamed 'name' field in SmpCacheProperties to 'cache', since the
>    type and level of the cache in SMP system could be able to specify
>    all of these kinds of cache explicitly enough.
>  * Renamed 'topo' field in SmpCacheProperties to 'topology'. (Markus)
>  * Returned error information when user repeats setting cache
>    properties. (Markus)
>  * Renamed SmpCacheLevelAndType to CacheLevelAndType, since this
>    representation is general across SMP or hybrid system.
>  * Dropped machine_check_smp_cache_support() and did the check when
>    -machine parses smp-cache in machine_parse_smp_cache().
> 
> 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 (7):
>   hw/core: Make CPU topology enumeration arch-agnostic
>   qapi/qom: Define cache enumeration and properties
>   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
> 
>  hw/core/machine-smp.c      | 119 +++++++++++++++++++++++
>  hw/core/machine.c          |  44 +++++++++
>  hw/i386/pc.c               |   4 +
>  hw/i386/x86-common.c       |   4 +-
>  include/hw/boards.h        |  13 +++
>  include/hw/i386/topology.h |  22 +----
>  qapi/machine-common.json   |  96 ++++++++++++++++++-
>  qemu-options.hx            |  28 +++++-
>  target/i386/cpu.c          | 191 ++++++++++++++++++++++---------------
>  target/i386/cpu.h          |   4 +-
>  10 files changed, 425 insertions(+), 100 deletions(-)
> 
> -- 
> 2.34.1