linux-kernel - Re: [PATCH] arch_topology: support parsing cluster

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Message-ID: <bd746cf0-0fdd-1ee6-d394-67fffb5d9b58@arm.com>
Date:   Thu, 12 May 2022 11:52:09 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     王擎 <wangqing@...o.com>,
        Sudeep Holla <sudeep.holla@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arch_topology: support parsing cluster_id from DT

On 11/05/2022 11:38, 王擎 wrote:
> 
>>> From: Wang Qing <wangqing@...o.com>

[...]

>> Would have to be cluster_id = -1. 0 is a valid 2. level cluster.
>> Otherwise you're not removing the CLS data from CPU4 to CPU7 in the
>> `Armv9 with L2 complexes` cpu-map example I used for testing:
>>
>>                 cpu-map {
>>                         cluster0 {
>>                                 cluster0 {
>>                                         core0 {
>>                                                 cpu = <&cpu0>;
>>                                         };
>>                                         core1 {
>>                                                 cpu = <&cpu1>;
>>                                         };
>>                                 };
>>                                 cluster1 {
>>                                         core0 {
>>                                                 cpu = <&cpu2>;
>>                                         };
>>                                         core1 {
>>                                                 cpu = <&cpu3>;
>>                                         };
>>                                 };
>>                         };
>>                         cluster1 {
>>                                 core0 {
>>                                         cpu = <&cpu4>;
>>                                 };
>>                                 core1 {
>>                                         cpu = <&cpu5>;
>>                                 };
>>                                 core2 {
>>                                         cpu = <&cpu6>;
>>                                 };
>>                         };
>>                         cluster2 {
>>                                 core0 {
>>                                         cpu = <&cpu7>;
>>                                 };
>>                         };
>>                 };

[...]

>> Looks like you also need to adapt update_siblings_masks() to only set
>> cpu in &cpu_topo->thread_sibling and &cpuid_topo->thread_sibling when
>> `cpu_topo->thread_id != -1`.
>>
>> @@ -723,11 +723,11 @@ void update_siblings_masks(unsigned int cpuid)
>>                 cpumask_set_cpu(cpuid, &cpu_topo->core_sibling);
>>                 cpumask_set_cpu(cpu, &cpuid_topo->core_sibling);
>>
>> -               if (cpuid_topo->core_id != cpu_topo->core_id)
>> -                       continue;
>> -
>> -               cpumask_set_cpu(cpuid, &cpu_topo->thread_sibling);
>> -               cpumask_set_cpu(cpu, &cpuid_topo->thread_sibling);
>> +               if (cpu_topo->thread_id != -1 &&
>> +                   cpuid_topo->core_id == cpu_topo->core_id) {
>> +                       cpumask_set_cpu(cpuid, &cpu_topo->thread_sibling);
>> +                       cpumask_set_cpu(cpu, &cpuid_topo->thread_sibling);
>> +
> 
> This seems like another problem?

I don't think so. If you run a system with the cpu-map mentioned above
you get:

# cat /sys/kernel/debug/sched/domains/cpu0/domain*/name
SMT        <-- !!!
CLS
MC

root@...5579:~# cat /proc/schedstat | awk '{print $1 " " $2 }' | grep
^[cd] | head -5
cpu0 0
domain0 05 <-- !!!
domain1 07 <-- !!!
domain2 0f
domain3 ff

So you get an unwanted SMT level for CPU0-3 and messed-up cpumasks
without this change.