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Date:   Thu, 18 May 2023 07:57:14 +0530
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Subject: Re: [PATCH v2 0/2] arch/x86: Set L2 Cache ID on AMD and Hygon
 processors
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From:   K Prateek Nayak <kprateek.nayak@amd.com>
To:     linux-kernel@vger.kernel.org
Cc:     tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
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Gentle ping :)

On 4/13/2023 10:59 PM, K Prateek Nayak wrote:
> commit 66558b730f253 ("sched: Add cluster scheduler level for x86")
> defined cluster on x86 as the set of threads sharing the same L2 cache.
> cluster_id on x86, maps to the l2c_id which currently only Intel
> processors set.
> 
> This series sets the l2c_id on AMD and Hygon processors with
> X86_FEATURE_TOPOEXT, using the extended APIC ID and the
> "Cache Properties (L2)" CPUID (0x8000001D EAX). On AMD and Hygon
> processors without X86_FEATURE_TOPOEXT, current behavior will continue.
> 
> Following are the changes in value reported by
> "/sys/devices/system/cpu/cpuX/topology/cluster_id" on a 2P Milan system
> (2 x 64C/128T) where L2 is per-core and SMT sibling of CPU (X) is
> CPU ((X + 128) % 256).
> 
> - tip:x86/core
> 
>   $ for i in {0..255}; do\
>       echo -n "CPU$i cluster_id: ";\
>       cat /sys/devices/system/cpu/cpu$i/topology/cluster_id;\
>     done;
> 
>     CPU0 cluster_id: 65535
>     CPU1 cluster_id: 65535
>     CPU2 cluster_id: 65535
>     CPU3 cluster_id: 65535
>     CPU4 cluster_id: 65535
>     ...
>     CPU254 cluster_id: 65535
>     CPU255 cluster_id: 65535
> 
> - tip:x86/core + this series
> 
>   $ for i in {0..255}; do\
>       echo -n "CPU$i cluster_id: ";\
>       cat /sys/devices/system/cpu/cpu$i/topology/cluster_id;\
>     done;
> 
>     CPU0 cluster_id: 0
>     CPU1 cluster_id: 1
>     CPU2 cluster_id: 2
>     CPU3 cluster_id: 3
>     CPU4 cluster_id: 4
>     CPU5 cluster_id: 5
>     CPU6 cluster_id: 6
>     CPU7 cluster_id: 7
>     CPU8 cluster_id: 8
>     ...
>     CPU126 cluster_id: 126
>     CPU127 cluster_id: 127
>     CPU128 cluster_id: 0
>     CPU129 cluster_id: 1
>     CPU130 cluster_id: 2
>     CPU131 cluster_id: 3
>     CPU132 cluster_id: 4
>     CPU133 cluster_id: 5
>     CPU134 cluster_id: 6
>     CPU135 cluster_id: 7
>     CPU136 cluster_id: 8
>     ...
>     CPU254 cluster_id: 126
>     CPU255 cluster_id: 127
> 
> Note: Hygon maintainer Pu Wen <puwen@hygon.cn> has confirmed that the
> same strategy of setting l2c_id works for Hygon as well without
> requiring any change to the function
> (https://lore.kernel.org/lkml/20230411122348.GAZDVRVNvbbS8F5NUB@fat_crate.local/)
> Call to the same function has been added in the Hygon topology init path
> too. Pu Wen, can you please test this version too and let me know if the
> behavior is still as expected.
> 
> The series also adds documentation for clusters on x86 platforms and
> applies cleanly on top of tip:x86/core at commit ce3ba2af9695
> ("x86: Suppress KMSAN reports in arch_within_stack_frames()")
> 
> ---
> o v1->v2
>   - Improved documentation of cluster based on Peter's suggestion.
>   - Renamed cacheinfo_amd_init_l2c_id() to
>     cacheinfo_topoext_init_l2c_id() and added the call to same in
>     Hygon's topology init path.
>   - Collected tags for Patch 1.
> ---
> K Prateek Nayak (2):
>   arch/x86: Set L2 Cache ID on AMD and Hygon processors
>   x86/Documentation: Add documentation about cluster
> 
>  Documentation/x86/topology.rst   | 27 ++++++++++++++++++++++++
>  arch/x86/include/asm/cacheinfo.h |  1 +
>  arch/x86/kernel/cpu/amd.c        |  1 +
>  arch/x86/kernel/cpu/cacheinfo.c  | 36 ++++++++++++++++++++++++++++++++
>  arch/x86/kernel/cpu/hygon.c      |  1 +
>  5 files changed, 66 insertions(+)
> 

--
Thanks and Regards,
Prateek