Subject: Re: [PATCH v3 02/10] powerpc/smp: Merge Power9 topology with Power topology

From: Gautham R Shenoy <[email-masked]>
Date: Fri, 24 Jul 2020 12:36:29 +0530

On Thu, Jul 23, 2020 at 02:21:08PM +0530, Srikar Dronamraju wrote:
> A new sched_domain_topology_level was added just for Power9. However the
> same can be achieved by merging powerpc_topology with power9_topology
> and makes the code more simpler especially when adding a new sched
> domain.
> 
> Cc: linuxppc-dev <[email-masked]>
> Cc: LKML <[email-masked]>
> Cc: Michael Ellerman <[email-masked]>
> Cc: Nicholas Piggin <[email-masked]>
> Cc: Anton Blanchard <[email-masked]>
> Cc: Oliver O'Halloran <[email-masked]>
> Cc: Nathan Lynch <[email-masked]>
> Cc: Michael Neuling <[email-masked]>
> Cc: Gautham R Shenoy <[email-masked]>
> Cc: Ingo Molnar <[email-masked]>
> Cc: Peter Zijlstra <[email-masked]>
> Cc: Valentin Schneider <[email-masked]>
> Cc: Jordan Niethe <[email-masked]>
> Signed-off-by: Srikar Dronamraju <[email-masked]>

LGTM.

Reviewed-by: Gautham R. Shenoy <[email-masked]>

> ---
> Changelog v1 -> v2:
> 	Replaced a reference to cpu_smt_mask with per_cpu(cpu_sibling_map, cpu)
> 	since cpu_smt_mask is only defined under CONFIG_SCHED_SMT
> 
>  arch/powerpc/kernel/smp.c | 33 ++++++++++-----------------------
>  1 file changed, 10 insertions(+), 23 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> index edf94ca64eea..283a04e54f52 100644
> --- a/arch/powerpc/kernel/smp.c
> +++ b/arch/powerpc/kernel/smp.c
> @@ -1313,7 +1313,7 @@ int setup_profiling_timer(unsigned int multiplier)
>  }
> 
>  #ifdef CONFIG_SCHED_SMT
> -/* cpumask of CPUs with asymetric SMT dependancy */
> +/* cpumask of CPUs with asymmetric SMT dependency */
>  static int powerpc_smt_flags(void)
>  {
>  	int flags = SD_SHARE_CPUCAPACITY | SD_SHARE_PKG_RESOURCES;
> @@ -1326,14 +1326,6 @@ static int powerpc_smt_flags(void)
>  }
>  #endif
> 
> -static struct sched_domain_topology_level powerpc_topology[] = {
> -#ifdef CONFIG_SCHED_SMT
> -	{ cpu_smt_mask, powerpc_smt_flags, SD_INIT_NAME(SMT) },
> -#endif
> -	{ cpu_cpu_mask, SD_INIT_NAME(DIE) },
> -	{ NULL, },
> -};
> -
>  /*
>   * P9 has a slightly odd architecture where pairs of cores share an L2 cache.
>   * This topology makes it *much* cheaper to migrate tasks between adjacent cores
> @@ -1351,7 +1343,13 @@ static int powerpc_shared_cache_flags(void)
>   */
>  static const struct cpumask *shared_cache_mask(int cpu)
>  {
> -	return cpu_l2_cache_mask(cpu);
> +	if (shared_caches)
> +		return cpu_l2_cache_mask(cpu);
> +
> +	if (has_big_cores)
> +		return cpu_smallcore_mask(cpu);
> +
> +	return per_cpu(cpu_sibling_map, cpu);
>  }
> 
>  #ifdef CONFIG_SCHED_SMT
> @@ -1361,7 +1359,7 @@ static const struct cpumask *smallcore_smt_mask(int cpu)
>  }
>  #endif
> 
> -static struct sched_domain_topology_level power9_topology[] = {
> +static struct sched_domain_topology_level powerpc_topology[] = {
>  #ifdef CONFIG_SCHED_SMT
>  	{ cpu_smt_mask, powerpc_smt_flags, SD_INIT_NAME(SMT) },
>  #endif
> @@ -1386,21 +1384,10 @@ void __init smp_cpus_done(unsigned int max_cpus)
>  #ifdef CONFIG_SCHED_SMT
>  	if (has_big_cores) {
>  		pr_info("Big cores detected but using small core scheduling\n");
> -		power9_topology[0].mask = smallcore_smt_mask;
>  		powerpc_topology[0].mask = smallcore_smt_mask;
>  	}
>  #endif
> -	/*
> -	 * If any CPU detects that it's sharing a cache with another CPU then
> -	 * use the deeper topology that is aware of this sharing.
> -	 */
> -	if (shared_caches) {
> -		pr_info("Using shared cache scheduler topology\n");
> -		set_sched_topology(power9_topology);
> -	} else {
> -		pr_info("Using standard scheduler topology\n");
> -		set_sched_topology(powerpc_topology);
> -	}
> +	set_sched_topology(powerpc_topology);
>  }
> 
>  #ifdef CONFIG_HOTPLUG_CPU
> -- 
> 2.18.2
>