linux-kernel - [PATCH 0/2] arch/x86: Set L2 Cache ID on AMD processors

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Date:   Mon, 10 Apr 2023 22:05:25 +0530
From:   K Prateek Nayak <kprateek.nayak@....com>
To:     <linux-kernel@...r.kernel.org>
CC:     <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
        <dave.hansen@...ux.intel.com>, <hpa@...or.com>, <corbet@....net>,
        <jgross@...e.com>, <andrew.cooper3@...rix.com>,
        <peterz@...radead.org>, <Jason@...c4.com>,
        <thomas.lendacky@....com>, <puwen@...on.cn>, <x86@...nel.org>,
        <linux-doc@...r.kernel.org>
Subject: [PATCH 0/2] arch/x86: Set L2 Cache ID on AMD processors

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 processors with X86_FEATURE_TOPOEXT,
using the extended APIC ID and the "Cache Properties (L2)" CPUID
(0x8000001D EAX). On AMD 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 level 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, theoretically, should be able to set the l2c_id using the
same cacheinfo_amd_init_l2c_id() function being added in Patch 1. Since
I do not have access to a Hygon machine to verify my theory, ccing Hygon
maintainer Pu Wen <puwen@...on.cn> for l2c_id enablement on Hygon.

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()")

---
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   | 31 +++++++++++++++++++++
 arch/x86/include/asm/cacheinfo.h |  1 +
 arch/x86/kernel/cpu/amd.c        |  1 +
 arch/x86/kernel/cpu/cacheinfo.c  | 47 ++++++++++++++++++++++++++++++++
 arch/x86/kernel/cpu/hygon.c      |  1 +
 5 files changed, 81 insertions(+)

-- 
2.34.1