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

[Oleksandr Natalenko <oleksandr@natalenko.name>]

Hello.

On pondělí 10. dubna 2023 18:35:25 CEST 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 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@hygon.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(+)

Having the following CPU:

```
Architecture:            x86_64
CPU op-mode(s):        32-bit, 64-bit
Address sizes:         48 bits physical, 48 bits virtual
Byte Order:            Little Endian
CPU(s):                  32
On-line CPU(s) list:   0-31
Vendor ID:               AuthenticAMD
Model name:            AMD Ryzen 9 5950X 16-Core Processor
CPU family:          25
Model:               33
Thread(s) per core:  2
Core(s) per socket:  16
Socket(s):           1
Stepping:            2
Frequency boost:     enabled
CPU(s) scaling MHz:  37%
CPU max MHz:         5084,0000
CPU min MHz:         550,0000
BogoMIPS:            6789,07
Flags:               fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_
tsc rep_good nopl nonstop_tsc cpuid extd_apicid aperfmperf rapl pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 x2apic movbe popcnt aes xsave avx f16c r
drand lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt tce topoext perfctr_core perfctr_nb bpext perfctr_l
lc mwaitx cpb cat_l3 cdp_l3 hw_pstate ssbd mba ibrs ibpb stibp vmmcall fsgsbase bmi1 avx2 smep bmi2 erms invpcid cqm rdt_a rdseed adx smap clflushopt clwb
sha_ni xsaveopt xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local clzero irperf xsaveerptr rdpru wbnoinvd arat npt lbrv svm_lock nrip
_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold avic v_vmsave_vmload vgif v_spec_ctrl umip pku ospke vaes vpclmulqdq rdpid ove
rflow_recov succor smca fsrm
Virtualization features:
Virtualization:        AMD-V
Caches (sum of all):
L1d:                   512 KiB (16 instances)
L1i:                   512 KiB (16 instances)
L2:                    8 MiB (16 instances)
L3:                    64 MiB (2 instances)
NUMA:
NUMA node(s):          1
NUMA node0 CPU(s):     0-31
Vulnerabilities:
Itlb multihit:         Not affected
L1tf:                  Not affected
Mds:                   Not affected
Meltdown:              Not affected
Mmio stale data:       Not affected
Retbleed:              Not affected
Spec store bypass:     Mitigation; Speculative Store Bypass disabled via prctl
Spectre v1:            Mitigation; usercopy/swapgs barriers and __user pointer sanitization
Spectre v2:            Mitigation; Retpolines, IBPB conditional, IBRS_FW, STIBP always-on, RSB filling, PBRSB-eIBRS Not affected
Srbds:                 Not affected
Tsx async abort:       Not affected
```

Without the series:

```
/sys/devices/system/cpu/cpu0/topology/cluster_id:65535
/sys/devices/system/cpu/cpu1/topology/cluster_id:65535
/sys/devices/system/cpu/cpu2/topology/cluster_id:65535
/sys/devices/system/cpu/cpu3/topology/cluster_id:65535
/sys/devices/system/cpu/cpu4/topology/cluster_id:65535
/sys/devices/system/cpu/cpu5/topology/cluster_id:65535
/sys/devices/system/cpu/cpu6/topology/cluster_id:65535
/sys/devices/system/cpu/cpu7/topology/cluster_id:65535
/sys/devices/system/cpu/cpu8/topology/cluster_id:65535
/sys/devices/system/cpu/cpu9/topology/cluster_id:65535
/sys/devices/system/cpu/cpu10/topology/cluster_id:65535
/sys/devices/system/cpu/cpu11/topology/cluster_id:65535
/sys/devices/system/cpu/cpu12/topology/cluster_id:65535
/sys/devices/system/cpu/cpu13/topology/cluster_id:65535
/sys/devices/system/cpu/cpu14/topology/cluster_id:65535
/sys/devices/system/cpu/cpu15/topology/cluster_id:65535
/sys/devices/system/cpu/cpu16/topology/cluster_id:65535
/sys/devices/system/cpu/cpu17/topology/cluster_id:65535
/sys/devices/system/cpu/cpu18/topology/cluster_id:65535
/sys/devices/system/cpu/cpu19/topology/cluster_id:65535
/sys/devices/system/cpu/cpu20/topology/cluster_id:65535
/sys/devices/system/cpu/cpu21/topology/cluster_id:65535
/sys/devices/system/cpu/cpu22/topology/cluster_id:65535
/sys/devices/system/cpu/cpu23/topology/cluster_id:65535
/sys/devices/system/cpu/cpu24/topology/cluster_id:65535
/sys/devices/system/cpu/cpu25/topology/cluster_id:65535
/sys/devices/system/cpu/cpu26/topology/cluster_id:65535
/sys/devices/system/cpu/cpu27/topology/cluster_id:65535
/sys/devices/system/cpu/cpu28/topology/cluster_id:65535
/sys/devices/system/cpu/cpu29/topology/cluster_id:65535
/sys/devices/system/cpu/cpu30/topology/cluster_id:65535
/sys/devices/system/cpu/cpu31/topology/cluster_id:65535
```

With the series:

```
/sys/devices/system/cpu/cpu0/topology/cluster_id:0
/sys/devices/system/cpu/cpu1/topology/cluster_id:1
/sys/devices/system/cpu/cpu2/topology/cluster_id:2
/sys/devices/system/cpu/cpu3/topology/cluster_id:3
/sys/devices/system/cpu/cpu4/topology/cluster_id:4
/sys/devices/system/cpu/cpu5/topology/cluster_id:5
/sys/devices/system/cpu/cpu6/topology/cluster_id:6
/sys/devices/system/cpu/cpu7/topology/cluster_id:7
/sys/devices/system/cpu/cpu8/topology/cluster_id:8
/sys/devices/system/cpu/cpu9/topology/cluster_id:9
/sys/devices/system/cpu/cpu10/topology/cluster_id:10
/sys/devices/system/cpu/cpu11/topology/cluster_id:11
/sys/devices/system/cpu/cpu12/topology/cluster_id:12
/sys/devices/system/cpu/cpu13/topology/cluster_id:13
/sys/devices/system/cpu/cpu14/topology/cluster_id:14
/sys/devices/system/cpu/cpu15/topology/cluster_id:15
/sys/devices/system/cpu/cpu16/topology/cluster_id:0
/sys/devices/system/cpu/cpu17/topology/cluster_id:1
/sys/devices/system/cpu/cpu18/topology/cluster_id:2
/sys/devices/system/cpu/cpu19/topology/cluster_id:3
/sys/devices/system/cpu/cpu20/topology/cluster_id:4
/sys/devices/system/cpu/cpu21/topology/cluster_id:5
/sys/devices/system/cpu/cpu22/topology/cluster_id:6
/sys/devices/system/cpu/cpu23/topology/cluster_id:7
/sys/devices/system/cpu/cpu24/topology/cluster_id:8
/sys/devices/system/cpu/cpu25/topology/cluster_id:9
/sys/devices/system/cpu/cpu26/topology/cluster_id:10
/sys/devices/system/cpu/cpu27/topology/cluster_id:11
/sys/devices/system/cpu/cpu28/topology/cluster_id:12
/sys/devices/system/cpu/cpu29/topology/cluster_id:13
/sys/devices/system/cpu/cpu30/topology/cluster_id:14
/sys/devices/system/cpu/cpu31/topology/cluster_id:15
```

Hence,

Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>

Thanks.

-- 
Oleksandr Natalenko (post-factum)