linux-kernel - Re: [PATCH RESEND 1/3] topology: Represent clusters of CPUs within a die

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Date:   Tue, 05 Oct 2021 17:33:59 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Barry Song <21cnbao@...il.com>, dietmar.eggemann@....com,
        linux-kernel@...r.kernel.org, mingo@...hat.com,
        peterz@...radead.org, vincent.guittot@...aro.org
Cc:     aubrey.li@...ux.intel.com, bp@...en8.de, bristot@...hat.com,
        bsegall@...gle.com, catalin.marinas@....com,
        gregkh@...uxfoundation.org, guodong.xu@...aro.org, hpa@...or.com,
        jonathan.cameron@...wei.com, juri.lelli@...hat.com,
        lenb@...nel.org, linux-acpi@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linuxarm@...wei.com,
        mark.rutland@....com, mgorman@...e.de, msys.mizuma@...il.com,
        prime.zeng@...ilicon.com, rjw@...ysocki.net, rostedt@...dmis.org,
        song.bao.hua@...ilicon.com, sudeep.holla@....com,
        tglx@...utronix.de, rafael@...nel.org, tim.c.chen@...ux.intel.com,
        will@...nel.org, x86@...nel.org, yangyicong@...wei.com,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Tian Tao <tiantao6@...ilicon.com>
Subject: Re: [PATCH RESEND 1/3] topology: Represent clusters of CPUs within a die

On 24/09/21 20:51, Barry Song wrote:
>  void update_siblings_masks(unsigned int cpuid)
>  {
>       struct cpu_topology *cpu_topo, *cpuid_topo = &cpu_topology[cpuid];
> @@ -617,6 +622,11 @@ void update_siblings_masks(unsigned int cpuid)
>               if (cpuid_topo->package_id != cpu_topo->package_id)
>                       continue;
>
> +		if (cpuid_topo->cluster_id == cpu_topo->cluster_id) {
> +			cpumask_set_cpu(cpu, &cpuid_topo->cluster_sibling);
> +			cpumask_set_cpu(cpuid, &cpu_topo->cluster_sibling);
> +		}
> +

Hm so without cluster information (e.g. DT system), we have
->cluster_id=-1, we'll essentially copy the package mask into the cluster
mask.

The exposed cluster mask is still <= package mask which is sensible. Are we
fine with that, or do we need/want the mask to be empty in the -1 case? I'm
guessing userspace tools should check for either id!=-1 or if the exclusive
disjucntion of cluster vs package masks is non-empty.