In x86, module is the topology level above core, which contains a set
of cores that share certain resources (in current products, the resource
usually includes L2 cache, as well as module scoped features and MSRs).
Though smp.clusters could also share the L2 cache resource [1], there
are following reasons that drive us to introduce the new smp.modules:
* As the CPU topology abstraction in device tree [2], 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.
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, place the module between the cluster and the core:
drawer/book/socket/die/cluster/module/core/thread
With the above topological hierarchy order, introduce module level
support in MachineState and MachineClass.
[1]: https://lore.kernel.org/qemu-devel/c3d68005-54e0-b8fe-8dc1-5989fe3c7e69@huawei.com/
[2]: https://www.kernel.org/doc/Documentation/devicetree/bindings/cpu/cpu-topology.txt
Suggested-by: Xiaoyao Li <xiaoyao.li@intel.com>
Tested-by: Yongwei Ma <yongwei.ma@intel.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Tested-by: Babu Moger <babu.moger@amd.com>
Message-ID: <20240424154929.1487382-2-zhao1.liu@intel.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
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