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

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Message-ID: <CAGsJ_4ycKDfFY+LoaUBJ5huH8+kUsGGsC1po4DDQQPU5-ikf8A@mail.gmail.com>
Date:   Wed, 6 Oct 2021 23:50:35 +1300
From:   Barry Song <21cnbao@...il.com>
To:     Valentin Schneider <valentin.schneider@....com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Ben Segall <bsegall@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Guodong Xu <guodong.xu@...aro.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Jonathan Cameron <jonathan.cameron@...wei.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        "Cc: Len Brown" <lenb@...nel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        LAK <linux-arm-kernel@...ts.infradead.org>,
        Linuxarm <linuxarm@...wei.com>,
        Mark Rutland <mark.rutland@....com>,
        Mel Gorman <mgorman@...e.de>, msys.mizuma@...il.com,
        "Zengtao (B)" <prime.zeng@...ilicon.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Steven Rostedt <rostedt@...dmis.org>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Sudeep Holla <sudeep.holla@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Will Deacon <will@...nel.org>, x86 <x86@...nel.org>,
        yangyicong <yangyicong@...wei.com>,
        Tian Tao <tiantao6@...ilicon.com>
Subject: Re: [PATCH RESEND 1/3] topology: Represent clusters of CPUs within a die

On Wed, Oct 6, 2021 at 9:43 AM Barry Song <21cnbao@...il.com> wrote:
>
> On Wed, Oct 6, 2021 at 5:34 AM Valentin Schneider
> <valentin.schneider@....com> wrote:
> >
> > 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.
>
> Hi Valentin,
> Yep, this is a very good question. I'd like change the code to:
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index 7cb31d959f33..fc0836f460fb 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -622,7 +622,8 @@ 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) {
> +               if (cpuid_topo->cluster_id == cpu_topo->cluster_id &&
> +                   cpuid_topo->cluster_id != -1) {
>                         cpumask_set_cpu(cpu, &cpuid_topo->cluster_sibling);
>                         cpumask_set_cpu(cpuid, &cpu_topo->cluster_sibling);
>                 }
>

Hi Peter,
Would you like to change this line in your tree? Or do you want me to send
a new patchset with this small change?

> This should be consistent with Tim's patch3/3 for x86 in case
> id is BAD_APICID:
> static bool match_l2c(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o)
> {
>         ...
>         /* Do not match if we do not have a valid APICID for cpu: */
>         if (per_cpu(cpu_l2c_id, cpu1) == BAD_APICID)
>                 return false;
>         ...
> }

Thanks
Barry