Re: [PATCH v3 4/7] arm, sched/topology: Remove SD_SHARE_POWERDOMAIN

[Valentin Schneider <valentin.schneider@arm.com>]

On 02/07/20 17:44, Dietmar Eggemann wrote:
> On 01/07/2020 21:06, Valentin Schneider wrote:
>> This flag was introduced in 2014 by commit
>>
>>   d77b3ed5c9f8 ("sched: Add a new SD_SHARE_POWERDOMAIN for sched_domain")
>>
>> but AFAIA it was never leveraged by the scheduler. The closest thing I can
>> think of is EAS caring about frequency domains, and it does that by
>> leveraging performance domains.
>
> ... and even this was purely out of tree (SD_SHARE_CAP_STATES).
>
>> Remove the flag.
>>
>> Suggested-by: Morten Rasmussen <morten.rasmussen@arm.com>
>> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
>> ---
>>  arch/arm/kernel/topology.c     |  2 +-
>>  include/linux/sched/sd_flags.h | 20 ++++++--------------
>>  kernel/sched/topology.c        | 10 +++-------
>>  3 files changed, 10 insertions(+), 22 deletions(-)
>>
>> diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
>> index b5adaf744630..353f3ee660e4 100644
>> --- a/arch/arm/kernel/topology.c
>> +++ b/arch/arm/kernel/topology.c
>> @@ -243,7 +243,7 @@ void store_cpu_topology(unsigned int cpuid)
>>
>>  static inline int cpu_corepower_flags(void)
>>  {
>> -	return SD_SHARE_PKG_RESOURCES  | SD_SHARE_POWERDOMAIN;
>> +	return SD_SHARE_PKG_RESOURCES;
>>  }
>>
>>  static struct sched_domain_topology_level arm_topology[] = {
>
> I guess with SD_SHARE_POWERDOMAIN gone, arch arm can even use the default_topology[]:

That does look like it! I never noticed we declared this GMC topology
level. Given it uses the thread_sibling mask, and that no (upstream) arm DT
uses the thread topology binding, I guess that makes sense.

>
> diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
> index b5adaf744630..87dd193165cc 100644
> --- a/arch/arm/kernel/topology.c
> +++ b/arch/arm/kernel/topology.c
> @@ -241,20 +241,6 @@ void store_cpu_topology(unsigned int cpuid)
>         update_siblings_masks(cpuid);
>  }
>
> -static inline int cpu_corepower_flags(void)
> -{
> -       return SD_SHARE_PKG_RESOURCES  | SD_SHARE_POWERDOMAIN;
> -}
> -
> -static struct sched_domain_topology_level arm_topology[] = {
> -#ifdef CONFIG_SCHED_MC
> -       { cpu_corepower_mask, cpu_corepower_flags, SD_INIT_NAME(GMC) },
> -       { cpu_coregroup_mask, cpu_core_flags, SD_INIT_NAME(MC) },
> -#endif
> -       { cpu_cpu_mask, SD_INIT_NAME(DIE) },
> -       { NULL, },
> -};
> -
>  /*
>   * init_cpu_topology is called at boot when only one cpu is running
>   * which prevent simultaneous write access to cpu_topology array
> @@ -265,7 +251,4 @@ void __init init_cpu_topology(void)
>         smp_wmb();
>
>         parse_dt_topology();
> -
> -       /* Set scheduler topology descriptor */
> -       set_sched_topology(arm_topology);
>  }