Re: [PATCH v9 00/21] Introduce smp.modules for x86 in QEMU

[Zhao Liu <zhao1.liu@linux.intel.com>]

Hi Paolo & Michael,

BTW, may I ask if this series could land in v9.0? ;-)

Thanks,
Zhao

On Tue, Feb 27, 2024 at 06:32:10PM +0800, Zhao Liu wrote:
> Date: Tue, 27 Feb 2024 18:32:10 +0800
> From: Zhao Liu <zhao1.liu@linux.intel.com>
> Subject: [PATCH v9 00/21] Introduce smp.modules for x86 in QEMU
> X-Mailer: git-send-email 2.34.1
> 
> From: Zhao Liu <zhao1.liu@intel.com>
> 
> Hi list,
> 
> This is the our v9 patch series, rebased on the master branch at the
> commit 03d496a992d9 ("Merge tag 'pull-qapi-2024-02-26' of
> https://repo.or.cz/qemu/armbru into staging").
> 
> Compared with v8 [1], v9 mainly added more module description in commit
> message and added missing smp.modules description/documentation.
> 
> With the general introduction (with origial cluster level) of this
> secries in v7 [2] cover letter, the following sections are mainly about
> the description of the newly added smp.modules (since v8, changed x86
> cluster support to module) as supplement.
> 
> Since v4 [3], we've dropped the original L2 cache command line option
> (to configure L2 cache topology) and now we have the new RFC [4] to
> support the general cache topology configuration (as the supplement to
> this series).
> 
> Welcome your comments!
> 
> 
> Why We Need a New CPU Topology Level
> ====================================
> 
> For the discussion in v7 about whether we should reuse current
> smp.clusters for x86 module, the core point is what's the essential
> differences between x86 module and general cluster.
> 
> Since, cluster (for ARM/riscv) lacks a comprehensive and rigorous
> hardware definition, and judging from the description of smp.clusters
> [5] when it was introduced by QEMU, x86 module is very similar to
> general smp.clusters: they are all a layer above existing core level
> to organize the physical cores and share L2 cache.
> 
> But there are following reasons that drive us to introduce the new
> smp.modules:
> 
>   * As the CPU topology abstraction in device tree [6], cluster supports
>     nesting (though currently QEMU hasn't support that). In contrast,
>     (x86) module does not support nesting.
> 
>   * Due to nesting, there is great flexibility in sharing resources
>     on cluster, rather than narrowing cluster down to sharing L2 (and
>     L3 tags) as the lowest topology level that contains cores.
> 
>   * Flexible nesting of cluster allows it to correspond to any level
>     between the x86 package and core.
> 
>   * In Linux kernel, x86's cluster only represents the L2 cache domain
>     but QEMU's smp.clusters is the CPU topology level. Linux kernel will
>     also expose module level topology information in sysfs for x86. To
>     avoid cluster ambiguity and keep a consistent CPU topology naming
>     style with the Linux kernel, we introduce module level for x86.
> 
> Based on the above considerations, and in order to eliminate the naming
> confusion caused by the mapping between general cluster and x86 module,
> we now formally introduce smp.modules as the new topology level.
> 
> 
> Where to Place Module in Existing Topology Levels
> =================================================
> 
> The module is, in existing hardware practice, the lowest layer that
> contains the core, while the cluster is able to have a higher topological
> scope than the module due to its nesting.
> 
> Therefore, we place the module between the cluster and the core:
> 
>     drawer/book/socket/die/cluster/module/core/thread
> 
> 
> Additional Consideration on CPU Topology
> ========================================
> 
> Beyond this patchset, nowadays, different arches have different topology
> requirements, and maintaining arch-agnostic general topology in SMP
> becomes to be an increasingly difficult thing due to differences in
> sharing resources and special flexibility (e.g., nesting):
> 
>   * It becomes difficult to put together all CPU topology hierarchies of
>     different arches to define complete topology order.
> 
>   * It also becomes complex to ensure the correctness of the topology
>     calculations.
>       - Now the max_cpus is calculated by multiplying all topology
>         levels, and too many topology levels can easily cause omissions.
> 
> Maybe we should consider implementing arch-specfic topology hierarchies.
> 
> 
> [1]: https://lore.kernel.org/qemu-devel/20240131101350.109512-1-zhao1.liu@linux.intel.com/
> [2]: https://lore.kernel.org/qemu-devel/20240108082727.420817-1-zhao1.liu@linux.intel.com/
> [3]: https://lore.kernel.org/qemu-devel/20231003085516-mutt-send-email-mst@kernel.org/
> [4]: https://lore.kernel.org/qemu-devel/20240220092504.726064-1-zhao1.liu@linux.intel.com/
> [5]: https://lore.kernel.org/qemu-devel/c3d68005-54e0-b8fe-8dc1-5989fe3c7e69@huawei.com/
> [6]: https://www.kernel.org/doc/Documentation/devicetree/bindings/cpu/cpu-topology.txt
> 
> Thanks and Best Regards,
> Zhao
> ---
> Changelog:
> 
> Changes since v8:
>  * Add the reason of why a new module level is needed in commit message.
>    (Markus).
>  * Add the description about how Linux kernel supports x86 module level
>    in commit message. (Daniel)
>  * Add module description in qemu_smp_opts.
>  * Add missing "modules" parameter of -smp example in documentation.
>  * Add Philippe's reviewed-by tag.
> 
> Changes since v7 (main changes):
>  * Introduced smp.modules as a new CPU topology level. (Xiaoyao)
>  * Fixed calculations of cache_info_passthrough case in the
>    patch "i386/cpu: Use APIC ID info to encode cache topo in
>    CPUID[4]". (Xiaoyao)
>  * Moved the patch "i386/cpu: Use APIC ID info get NumSharingCache
>    for CPUID[0x8000001D].EAX[bits 25:14]" after CPUID[4]'s similar
>    change ("i386/cpu: Use APIC ID offset to encode cache topo in
>    CPUID[4]"). (Xiaoyao)
>  * Introduced a bitmap in CPUX86State to cache available CPU topology
>    levels.
>  * Refactored the encode_topo_cpuid1f() to use traversal to search the
>    encoded level and avoid using static variables.
>  * Mapped x86 module to smp module instead of cluster.
>  * Dropped Michael/Babu's ACKed/Tested tags for most patches since the
>    code change.
> 
> Changes since v6:
>  * Updated the comment when check cluster-id. Since there's no
>    v8.2, the cluster-id support should at least start from v9.0.
>  * Rebased on commit d328fef93ae7 ("Merge tag 'pull-20231230' of
>    https://gitlab.com/rth7680/qemu into staging").
> 
> Changes since v5:
>  * The first four patches of v5 [1] have been merged, v6 contains
>    the remaining patches.
>  * Reabsed on the latest master.
>  * Updated the comment when check cluster-id. Since current QEMU is
>    v8.2, the cluster-id support should at least start from v8.3.
> 
> Changes since v4:
>  * Dropped the "x-l2-cache-topo" option. (Michael)
>  * Added A/R/T tags.
> 
> Changes since v3 (main changes):
>  * Exposed module level in CPUID[0x1F].
>  * Fixed compile warnings. (Babu)
>  * Fixed cache topology uninitialization bugs for some AMD CPUs. (Babu)
> 
> Changes since v2:
>  * Added "Tested-by", "Reviewed-by" and "ACKed-by" tags.
>  * Used newly added wrapped helper to get cores per socket in
>    qemu_init_vcpu().
> 
> Changes since v1:
>  * Reordered patches. (Yanan)
>  * Deprecated the patch to fix comment of machine_parse_smp_config().
>    (Yanan)
>  * Renamed test-x86-cpuid.c to test-x86-topo.c. (Yanan)
>  * Split the intel's l1 cache topology fix into a new separate patch.
>    (Yanan)
>  * Combined module_id and APIC ID for module level support into one
>    patch. (Yanan)
>  * Made cache_into_passthrough case of cpuid 0x04 leaf in
>  * cpu_x86_cpuid() used max_processor_ids_for_cache() and
>    max_core_ids_in_package() to encode CPUID[4]. (Yanan)
>  * Added the prefix "CPU_TOPO_LEVEL_*" for CPU topology level names.
>    (Yanan)
> ---
> Zhao Liu (20):
>   hw/core/machine: Introduce the module as a CPU topology level
>   hw/core/machine: Support modules in -smp
>   hw/core: Introduce module-id as the topology subindex
>   hw/core: Support module-id in numa configuration
>   i386/cpu: Fix i/d-cache topology to core level for Intel CPU
>   i386/cpu: Use APIC ID info to encode cache topo in CPUID[4]
>   i386/cpu: Use APIC ID info get NumSharingCache for
>     CPUID[0x8000001D].EAX[bits 25:14]
>   i386/cpu: Consolidate the use of topo_info in cpu_x86_cpuid()
>   i386/cpu: Introduce bitmap to cache available CPU topology levels
>   i386: Split topology types of CPUID[0x1F] from the definitions of
>     CPUID[0xB]
>   i386/cpu: Decouple CPUID[0x1F] subleaf with specific topology level
>   i386: Introduce module level cpu topology to CPUX86State
>   i386: Support modules_per_die in X86CPUTopoInfo
>   i386: Expose module level in CPUID[0x1F]
>   i386: Support module_id in X86CPUTopoIDs
>   i386/cpu: Introduce module-id to X86CPU
>   hw/i386/pc: Support smp.modules for x86 PC machine
>   i386: Add cache topology info in CPUCacheInfo
>   i386/cpu: Use CPUCacheInfo.share_level to encode CPUID[4]
>   i386/cpu: Use CPUCacheInfo.share_level to encode
>     CPUID[0x8000001D].EAX[bits 25:14]
> 
> Zhuocheng Ding (1):
>   tests: Add test case of APIC ID for module level parsing
> 
>  hw/core/machine-hmp-cmds.c |   4 +
>  hw/core/machine-smp.c      |  41 +++--
>  hw/core/machine.c          |  18 +++
>  hw/i386/pc.c               |   1 +
>  hw/i386/x86.c              |  67 ++++++--
>  include/hw/boards.h        |   4 +
>  include/hw/i386/topology.h |  60 +++++++-
>  qapi/machine.json          |   7 +
>  qemu-options.hx            |  18 ++-
>  system/vl.c                |   3 +
>  target/i386/cpu.c          | 304 +++++++++++++++++++++++++++++--------
>  target/i386/cpu.h          |  29 +++-
>  target/i386/kvm/kvm.c      |   3 +-
>  tests/unit/test-x86-topo.c |  56 ++++---
>  14 files changed, 489 insertions(+), 126 deletions(-)
> 
> -- 
> 2.34.1
> 
>