Hi Paolo,
I have a question before I do a new v12 rebase:
Since patch 5,6,7 fixed CPUID encoding way, should I add the compat
options for older machines to be compatible with past encoding behavior?
Thanks,
Zhao
On Wed, Apr 24, 2024 at 11:49:08PM +0800, Zhao Liu wrote:
> Date: Wed, 24 Apr 2024 23:49:08 +0800
> From: Zhao Liu <zhao1.liu@xxxxxxxxx>
> Subject: [PATCH v11 00/21] i386: Introduce smp.modules and clean up cache
> topology
> X-Mailer: git-send-email 2.34.1
>
> Hi maintainers,
>
> This is the my v11 patch series, rebased on the master branch at the
> commit 88daa112d4ed ("Merge tag 'migration-20240423-pull-request' of
> https://gitlab.com/peterx/qemu into staging").
>
> Since v10 didn't receive comment so v11 just rebase on the latest v9.0
> to resolve minor conflicts to facilitate maintainer. ;-)
>
> This is a larger series, and almost all patches (containing all the key
> changes) has gotten Reviewed-by and Acked-by, and tested from both Intel
> and AMD.
>
> Thank you all for your patience and help!
>
>
> Abstract
> ========
>
> Intel's hybrid Client platform and E core server platform introduce
> module level and share L2 cache on the module level, in order to
> configure the CPU/cache topology for the Guest to be consistent with
> Host's, this series did the following work:
> * Add now "module" CPU topology level for x86 CPU.
> * Refacter cache topology encoding for x86 CPU (This is base to
> support the L2 per module).
>
> So, this series is also necessary to support subsequent user
> configurations of cache topology (via -smp, [2]) and Intel heterogeneous
> CPU topology ([3] and [4]).
>
>
> Background
> ==========
>
> At present, x86 defaults L2 cache is shared in one core, but this is
> not enough. There're some platforms that multiple cores share the
> same L2 cache, e.g., Alder Lake-P shares L2 cache for one module of
> Atom cores, that is, every four Atom cores shares one L2 cache. On
> E core server platform, there's the similar L2 per module topology.
> Therefore, we need the new CPU topology level.
>
>
> Another reason is that Intel client hybrid architectures organize P
> cores and E cores via module, so a new CPU topology level is necessary
> to support hybrid CPU topology!
>
>
> Why We Introduce Module Instead of Reusing Cluster
> --------------------------------------------------
>
> 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
>
>
> Patch Series Overview
> =====================
>
> Introduction of Module Level in -smp
> ------------------------------------
>
> First, a new module level is introduced in the -smp related code to
> support the module topology in subsequent x86 parts.
>
> Users can specify the number of modules (in one die) for a PC machine
> with "-smp modules=*".
>
>
> Why not Share L2 Cache in Module Directly
> -----------------------------------------
>
> Though one of module's goals is to implement L2 cache per module,
> directly using module to define x86's L2 cache topology will cause the
> compatibility problem:
>
> Currently, x86 defaults that the L2 cache is shared in one core, which
> actually implies a default setting "cores per L2 cache is 1" and
> therefore implicitly defaults to having as many L2 caches as cores.
>
> For example (i386 PC machine):
> -smp 16,sockets=2,dies=2,cores=2,threads=2,maxcpus=16 (*)
>
> Considering the topology of the L2 cache, this (*) implicitly means "1
> core per L2 cache" and "2 L2 caches per die".
>
> If we use module to configure L2 cache topology with the new default
> setting "modules per L2 cache is 1", the above semantics will change
> to "2 cores per module" and "1 module per L2 cache", that is, "2
> cores per L2 cache".
>
> So the same command (*) will cause changes in the L2 cache topology,
> further affecting the performance of the virtual machine.
>
> Therefore, x86 should only treat module as a cpu topology level and
> avoid using it to change L2 cache by default for compatibility.
>
> Thereby, we need another way to allow user to configure cache topology,
> this is anther RFC [2].
>
>
> Module Level in CPUID
> ---------------------
>
> Linux kernel (from v6.4, with commit edc0a2b595765 ("x86/topology: Fix
> erroneous smp_num_siblings on Intel Hybrid platforms") is able to
> handle platforms with Module level enumerated via CPUID.1F.
>
> Expose the module level in CPUID[0x1F] (for Intel CPUs) if the machine
> has more than 1 modules since v3.
>
>
> New Cache Topology Info in CPUCacheInfo
> ---------------------------------------
>
> (This is in preparation for users being able to configure cache topology
> from the command line later on.)
>
> Currently, by default, the cache topology is encoded as:
> 1. i/d cache is shared in one core.
> 2. L2 cache is shared in one core.
> 3. L3 cache is shared in one die.
>
> This default general setting has caused a misunderstanding, that is, the
> cache topology is completely equated with a specific CPU topology, such
> as the connection between L2 cache and core level, and the connection
> between L3 cache and die level.
>
> In fact, the settings of these topologies depend on the specific
> platform and are not static. For example, on Alder Lake-P, every
> four Atom cores share the same L2 cache [3].
>
> Thus, in this patch set, we explicitly define the corresponding cache
> topology for different cache models and this has two benefits:
> 1. Easy to expand to new cache models with different topology in the
> future.
> 2. It can easily support custom cache topology by some command.
>
>
> Patch Description
> =================
>
> Patch 01-04: Add module support in -smp.
>
> Patch 05: Fix Intel L1 cache topology.
>
> Patch 06-08: Clean up cache topology related CPUID encoding and QEMU
> topology variables.
>
> Patch 09-11: Refactor CPUID[0x1F] (CPU topology) encoding to prepare to
> introduce module level.
>
> Patch 12-18: Add the module as the new CPU topology level in x86.
>
> Patch 19-21: Refactor cache topology encoding for Intel and AMD.
>
>
> Reference
> =========
>
> [1]: https://lore.kernel.org/qemu-devel/20240321144048.3699388-1-zhao1.liu@xxxxxxxxxxxxxxx/
> [2]: https://lore.kernel.org/qemu-devel/20240220092504.726064-1-zhao1.liu@xxxxxxxxxxxxxxx/
> [3]: https://lore.kernel.org/qemu-devel/20230213095035.158240-1-zhao1.liu@xxxxxxxxxxxxxxx/
> [4]: https://lore.kernel.org/qemu-devel/20231130144203.2307629-1-zhao1.liu@xxxxxxxxxxxxxxx/
>
>
> Thanks and Best Regards,
> Zhao
> ---
> Changelog:
>
> Changes since v10:
> * Rebased on commit 88daa11.
>
> Changes since v9:
> * Collected a/b, t/b and r/b tags.
> * Fixed typos.
> * Minor cleanup of code.
> * Added more comments and polished commit message.
>
> Changes since v8:
> * Added the reason of why a new module level is needed in commit
> message. (Markus).
> * Added the description about how Linux kernel supports x86 module
> level in commit message. (Daniel)
> * Added module description in qemu_smp_opts.
> * Added missing "modules" parameter of -smp example in documentation.
> * Added 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 also encode via
> APICID way. (Yanan)
> * 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 | 301 +++++++++++++++++++++++++++++--------
> target/i386/cpu.h | 29 +++-
> target/i386/kvm/kvm.c | 3 +-
> tests/unit/test-x86-topo.c | 56 ++++---
> 14 files changed, 490 insertions(+), 122 deletions(-)
>
> --
> 2.34.1
>
