linux-kernel - Re: [PATCH 2/3] topology/sysfs: export cluster attributes only if an architectures has support

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Date:   Mon, 29 Nov 2021 07:54:24 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Heiko Carstens <hca@...ux.ibm.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Len Brown <len.brown@...el.com>,
        Thomas Richter <tmricht@...ux.ibm.com>,
        Ian Rogers <irogers@...gle.com>
Subject: Re: [PATCH 2/3] topology/sysfs: export cluster attributes only if an
 architectures has support

On Sun, Nov 28, 2021 at 10:22:20PM +0100, Heiko Carstens wrote:
> The cluster_id and cluster_cpus topology sysfs attributes have been
> added with c5e22feffdd7 ("topology: Represent clusters of CPUs within
> a die").
> 
> They are currently only used for x86, arm64, and riscv (via generic
> arch topology), however they are still present with bogus default
> values for all other architectures. Instead of enforcing such new
> sysfs attributes to all architectures, make them only optional visible
> if an architecture opts in by defining both the topology_cluster_id
> and topology_cluster_cpumask attributes.
> 
> This is similar to what was done when the book and drawer topology
> levels were introduced: avoid useless and therefore confusing sysfs
> attributes for architectures which cannot make use of them.
> 
> This should not break any existing applications, since this is a
> new interface introduced with the v5.16 merge window.
> 
> Signed-off-by: Heiko Carstens <hca@...ux.ibm.com>
> ---
>  Documentation/admin-guide/cputopology.rst | 4 ++--
>  drivers/base/topology.c                   | 8 ++++++++
>  include/linux/topology.h                  | 2 ++
>  3 files changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/admin-guide/cputopology.rst b/Documentation/admin-guide/cputopology.rst
> index c68d07533c45..ad2238b41439 100644
> --- a/Documentation/admin-guide/cputopology.rst
> +++ b/Documentation/admin-guide/cputopology.rst
> @@ -11,8 +11,8 @@ Architecture-neutral, drivers/base/topology.c, exports these attributes.
>  However, the book and drawer related sysfs files will only be created if
>  CONFIG_SCHED_BOOK and CONFIG_SCHED_DRAWER are selected, respectively.
>  
> -The die hierarchy related sysfs files will only be created if an architecture
> -provides the related macros as described below.
> +The die and cluster hierarchy related sysfs files will only be created if an
> +architecture provides the related macros as described below.
>  
>  CONFIG_SCHED_BOOK and CONFIG_SCHED_DRAWER are currently only used on s390,
>  where they reflect the cpu and cache hierarchy.
> diff --git a/drivers/base/topology.c b/drivers/base/topology.c
> index 7fa5a7fbef25..1a288eac2c44 100644
> --- a/drivers/base/topology.c
> +++ b/drivers/base/topology.c
> @@ -50,8 +50,10 @@ define_id_show_func(die_id);
>  static DEVICE_ATTR_RO(die_id);
>  #endif
>  
> +#ifndef topology_cluster_no_sysfs

Same comment here, do not enable an option that disables something :)

thanks,

greg k-h