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Tsirkin" To: Zhao Liu Cc: Eduardo Habkost , Marcel Apfelbaum , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Yanan Wang , Richard Henderson , Paolo Bonzini , Marcelo Tosatti , qemu-devel@nongnu.org, kvm@vger.kernel.org, Zhenyu Wang , Xiaoyao Li , Babu Moger , Zhao Liu Subject: Re: [PATCH v4 00/21] Support smp.clusters for x86 in QEMU Message-ID: <20231018080635-mutt-send-email-mst@kernel.org> References: <20230914072159.1177582-1-zhao1.liu@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230914072159.1177582-1-zhao1.liu@linux.intel.com> Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, Sep 14, 2023 at 03:21:38PM +0800, Zhao Liu wrote: > From: Zhao Liu > > Hi list, > > (CC kvm@vger.kernel.org for better browsing.) > > This is the our v4 patch series, rebased on the master branch at the > commit 9ef497755afc2 ("Merge tag 'pull-vfio-20230911' of > https://github.com/legoater/qemu into staging"). > > Comparing with v3 [1], v4 mainly refactors the CPUID[0x1F] encoding and > exposes module level in CPUID[0x1F] with these new patches: > > * [PATCH v4 08/21] i386: Split topology types of CPUID[0x1F] from the > definitions of CPUID[0xB] > * [PATCH v4 09/21] i386: Decouple CPUID[0x1F] subleaf with specific > topology level > * [PATCH v4 12/21] i386: Expose module level in CPUID[0x1F] > > v4 also fixes compile warnings and fixes cache topology uninitialization > bugs for some AMD CPUs. > > Welcome your comments! Acked-by: Michael S. Tsirkin > > # Introduction > > This series add the cluster support for x86 PC machine, which allows > x86 can use smp.clusters to configure the module level CPU topology > of x86. > > And since the compatibility issue (see section: ## Why not share L2 > cache in cluster directly), this series also introduce a new command > to adjust the topology of the x86 L2 cache. > > Welcome your comments! > > > # Background > > The "clusters" parameter in "smp" is introduced by ARM [2], but x86 > hasn't supported it. > > 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 [3], that is, every four Atom cores shares one L2 cache. > Therefore, we need the new CPU topology level (cluster/module). > > Another reason is for hybrid architecture. cluster support not only > provides another level of topology definition in x86, but would also > provide required code change for future our hybrid topology support. > > > # Overview > > ## Introduction of module level for x86 > > "cluster" in smp is the CPU topology level which is between "core" and > die. > > For x86, the "cluster" in smp is corresponding to the module level [4], > which is above the core level. So use the "module" other than "cluster" > in x86 code. > > And please note that x86 already has a cpu topology level also named > "cluster" [4], this level is at the upper level of the package. Here, > the cluster in x86 cpu topology is completely different from the > "clusters" as the smp parameter. After the module level is introduced, > the cluster as the smp parameter will actually refer to the module level > of x86. > > > ## Why not share L2 cache in cluster directly > > Though "clusters" was introduced to help define L2 cache topology > [2], using cluster 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 cluster to configure L2 cache topology with the new default > setting "clusters per L2 cache is 1", the above semantics will change > to "2 cores per cluster" and "1 cluster 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 cluster as a cpu topology level and > avoid using it to change L2 cache by default for compatibility. > > > ## 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. > > We can configure CPUID.04H.02H (L2 cache topology) with module level by > a new command: > > "-cpu,x-l2-cache-topo=cluster" > > More information about this command, please see the section: "## New > property: x-l2-cache-topo". > > > ## New cache topology info in CPUCacheInfo > > 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 [2]. > > Thus, in this patch set, we explicitly define the corresponding cache > topology for different cpu models and this has two benefits: > 1. Easy to expand to new CPU models in the future, which has different > cache topology. > 2. It can easily support custom cache topology by some command (e.g., > x-l2-cache-topo). > > > ## New property: x-l2-cache-topo > > The property x-l2-cache-topo will be used to change the L2 cache > topology in CPUID.04H. > > Now it allows user to set the L2 cache is shared in core level or > cluster level. > > If user passes "-cpu x-l2-cache-topo=[core|cluster]" then older L2 cache > topology will be overrode by the new topology setting. > > Since CPUID.04H is used by Intel CPUs, this property is available on > Intel CPUs as for now. > > When necessary, it can be extended to CPUID[0x8000001D] for AMD CPUs. > > > # Patch description > > patch 1-2 Cleanups about coding style and test name. > > patch 3-5 Fixes about x86 topology and Intel l1 cache topology. > > patch 6-7 Cleanups about topology related CPUID encoding and QEMU > topology variables. > > patch 8-9 Refactor CPUID[0x1F] encoding to prepare to introduce module > level. > > patch 10-16 Add the module as the new CPU topology level in x86, and it > is corresponding to the cluster level in generic code. > > patch 17,18,20 Add cache topology information in cache models. > > patch 19 Update AMD CPUs' cache topology encoding. > > patch 21 Introduce a new command to configure L2 cache topology. > > > [1]: https://lists.gnu.org/archive/html/qemu-devel/2023-08/msg00022.html > [2]: https://patchew.org/QEMU/20211228092221.21068-1-wangyanan55@huawei.com/ > [3]: https://www.intel.com/content/www/us/en/products/platforms/details/alder-lake-p.html > [4]: SDM, vol.3, ch.9, 9.9.1 Hierarchical Mapping of Shared Resources. > > Best Regards, > Zhao > --- > Changelog: > > Changes since v3 (main changes): > * Expose module level in CPUID[0x1F]. > * Fix compile warnings. (Babu) > * Fixes cache topology uninitialization bugs for some AMD CPUs. (Babu) > > Changes since v2: > * Add "Tested-by", "Reviewed-by" and "ACKed-by" tags. > * Use 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) > * Rename 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) > * Make cache_into_passthrough case of cpuid 0x04 leaf in > * cpu_x86_cpuid() use max_processor_ids_for_cache() and > max_core_ids_in_package() to encode CPUID[4]. (Yanan) > * Add the prefix "CPU_TOPO_LEVEL_*" for CPU topology level names. > (Yanan) > --- > Zhao Liu (14): > i386: Fix comment style in topology.h > tests: Rename test-x86-cpuid.c to test-x86-topo.c > hw/cpu: Update the comments of nr_cores and nr_dies > i386/cpu: Fix i/d-cache topology to core level for Intel CPU > i386/cpu: Use APIC ID offset to encode cache topo in CPUID[4] > i386/cpu: Consolidate the use of topo_info in cpu_x86_cpuid() > i386: Split topology types of CPUID[0x1F] from the definitions of > CPUID[0xB] > i386: Decouple CPUID[0x1F] subleaf with specific topology level > i386: Expose module level in CPUID[0x1F] > i386: Add cache topology info in CPUCacheInfo > i386: Use CPUCacheInfo.share_level to encode CPUID[4] > i386: Use offsets get NumSharingCache for CPUID[0x8000001D].EAX[bits > 25:14] > i386: Use CPUCacheInfo.share_level to encode > CPUID[0x8000001D].EAX[bits 25:14] > i386: Add new property to control L2 cache topo in CPUID.04H > > Zhuocheng Ding (7): > softmmu: Fix CPUSTATE.nr_cores' calculation > i386: Introduce module-level cpu topology to CPUX86State > i386: Support modules_per_die in X86CPUTopoInfo > i386: Support module_id in X86CPUTopoIDs > i386/cpu: Introduce cluster-id to X86CPU > tests: Add test case of APIC ID for module level parsing > hw/i386/pc: Support smp.clusters for x86 PC machine > > MAINTAINERS | 2 +- > hw/i386/pc.c | 1 + > hw/i386/x86.c | 49 ++- > include/hw/core/cpu.h | 2 +- > include/hw/i386/topology.h | 68 ++-- > qemu-options.hx | 10 +- > softmmu/cpus.c | 2 +- > target/i386/cpu.c | 322 ++++++++++++++---- > target/i386/cpu.h | 46 ++- > target/i386/kvm/kvm.c | 2 +- > tests/unit/meson.build | 4 +- > .../{test-x86-cpuid.c => test-x86-topo.c} | 58 ++-- > 12 files changed, 437 insertions(+), 129 deletions(-) > rename tests/unit/{test-x86-cpuid.c => test-x86-topo.c} (73%) > > -- > 2.34.1