Re: [PATCH 09/11] Powerpc/smp: Create coregroup domain

[Gautham R Shenoy <ego@linux.vnet.ibm.com>]

On Tue, Jul 14, 2020 at 10:06:22AM +0530, Srikar Dronamraju wrote:
> Add percpu coregroup maps and masks to create coregroup domain.
> If a coregroup doesn't exist, the coregroup domain will be degenerated
> in favour of SMT/CACHE domain.
> 
> Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
> Cc: Michael Ellerman <michaele@au1.ibm.com>
> Cc: Nick Piggin <npiggin@au1.ibm.com>
> Cc: Oliver OHalloran <oliveroh@au1.ibm.com>
> Cc: Nathan Lynch <nathanl@linux.ibm.com>
> Cc: Michael Neuling <mikey@linux.ibm.com>
> Cc: Anton Blanchard <anton@au1.ibm.com>
> Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>
> Cc: Vaidyanathan Srinivasan <svaidy@linux.ibm.com>
> Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> ---
>  arch/powerpc/include/asm/topology.h | 10 ++++++++
>  arch/powerpc/kernel/smp.c           | 37 +++++++++++++++++++++++++++++
>  arch/powerpc/mm/numa.c              |  5 ++++
>  3 files changed, 52 insertions(+)
> 
> diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
> index 2db7ba789720..34812c35018e 100644
> --- a/arch/powerpc/include/asm/topology.h
> +++ b/arch/powerpc/include/asm/topology.h
> @@ -98,6 +98,7 @@ extern int stop_topology_update(void);
>  extern int prrn_is_enabled(void);
>  extern int find_and_online_cpu_nid(int cpu);
>  extern int timed_topology_update(int nsecs);
> +extern int cpu_to_coregroup_id(int cpu);
>  #else
>  static inline int start_topology_update(void)
>  {
> @@ -120,6 +121,15 @@ static inline int timed_topology_update(int nsecs)
>  	return 0;
>  }
> 
> +static inline int cpu_to_coregroup_id(int cpu)
> +{
> +#ifdef CONFIG_SMP
> +	return cpu_to_core_id(cpu);
> +#else
> +	return 0;
> +#endif
> +}
> +
>  #endif /* CONFIG_NUMA && CONFIG_PPC_SPLPAR */
> 
>  #include <asm-generic/topology.h>
> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> index ef19eeccd21e..bb25c13bbb79 100644
> --- a/arch/powerpc/kernel/smp.c
> +++ b/arch/powerpc/kernel/smp.c
> @@ -80,6 +80,7 @@ DEFINE_PER_CPU(cpumask_var_t, cpu_sibling_map);
>  DEFINE_PER_CPU(cpumask_var_t, cpu_smallcore_map);
>  DEFINE_PER_CPU(cpumask_var_t, cpu_l2_cache_map);
>  DEFINE_PER_CPU(cpumask_var_t, cpu_core_map);
> +DEFINE_PER_CPU(cpumask_var_t, cpu_coregroup_map);
> 
>  EXPORT_PER_CPU_SYMBOL(cpu_sibling_map);
>  EXPORT_PER_CPU_SYMBOL(cpu_l2_cache_map);
> @@ -91,6 +92,7 @@ enum {
>  	smt_idx,
>  #endif
>  	bigcore_idx,
> +	mc_idx,
>  	die_idx,
>  };
> 
> @@ -869,6 +871,21 @@ static const struct cpumask *smallcore_smt_mask(int cpu)
>  }
>  #endif
> 
> +static struct cpumask *cpu_coregroup_mask(int cpu)
> +{
> +	return per_cpu(cpu_coregroup_map, cpu);
> +}
> +
> +static bool has_coregroup_support(void)
> +{
> +	return coregroup_enabled;
> +}
> +
> +static const struct cpumask *cpu_mc_mask(int cpu)
> +{
> +	return cpu_coregroup_mask(cpu);
> +}
> +
>  static const struct cpumask *cpu_bigcore_mask(int cpu)
>  {
>  	return cpu_core_mask(cpu);
> @@ -879,6 +896,7 @@ static struct sched_domain_topology_level powerpc_topology[] = {
>  	{ cpu_smt_mask, powerpc_smt_flags, SD_INIT_NAME(SMT) },
>  #endif
>  	{ cpu_bigcore_mask, SD_INIT_NAME(BIGCORE) },
> +	{ cpu_mc_mask, SD_INIT_NAME(MC) },
>  	{ cpu_cpu_mask, SD_INIT_NAME(DIE) },
>  	{ NULL, },
>  };
> @@ -933,6 +951,10 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
>  					GFP_KERNEL, node);
>  		zalloc_cpumask_var_node(&per_cpu(cpu_core_map, cpu),
>  					GFP_KERNEL, node);
> +		if (has_coregroup_support())
> +			zalloc_cpumask_var_node(&per_cpu(cpu_coregroup_map, cpu),
> +						GFP_KERNEL, node);
> +
>  #ifdef CONFIG_NEED_MULTIPLE_NODES
>  		/*
>  		 * numa_node_id() works after this.
> @@ -950,6 +972,11 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
>  	cpumask_set_cpu(boot_cpuid, cpu_l2_cache_mask(boot_cpuid));
>  	cpumask_set_cpu(boot_cpuid, cpu_core_mask(boot_cpuid));
> 
> +	if (has_coregroup_support())
> +		cpumask_set_cpu(boot_cpuid, cpu_coregroup_mask(boot_cpuid));
> +	else
> +		powerpc_topology[mc_idx].mask = cpu_bigcore_mask;
> +

The else part could be moved to the common function where we are
modifying the other attributes of the topology array.


>  	init_big_cores();
>  	if (has_big_cores) {
>  		cpumask_set_cpu(boot_cpuid,
> @@ -1241,6 +1268,8 @@ static void remove_cpu_from_masks(int cpu)
>  		set_cpus_unrelated(cpu, i, cpu_sibling_mask);
>  		if (has_big_cores)
>  			set_cpus_unrelated(cpu, i, cpu_smallcore_mask);
> +		if (has_coregroup_support())
> +			set_cpus_unrelated(cpu, i, cpu_coregroup_mask);
>  	}
>  }
>  #endif
> @@ -1301,6 +1330,14 @@ static void add_cpu_to_masks(int cpu)
>  	add_cpu_to_smallcore_masks(cpu);
>  	update_mask_by_l2(cpu, cpu_l2_cache_mask);
> 
> +	if (has_coregroup_support()) {
> +		cpumask_set_cpu(cpu, cpu_coregroup_mask(cpu));
> +		for_each_cpu(i, cpu_online_mask) {
> +			if (cpu_to_coregroup_id(cpu) == cpu_to_coregroup_id(i))
> +				set_cpus_related(cpu, i, cpu_coregroup_mask);
> +		}
> +	}
> +
>  	if (pkg_id == -1) {
>  		struct cpumask *(*mask)(int) = cpu_sibling_mask;
> 
> diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
> index a43eab455be4..d9ab9da85eab 100644
> --- a/arch/powerpc/mm/numa.c
> +++ b/arch/powerpc/mm/numa.c
> @@ -1695,6 +1695,11 @@ static const struct proc_ops topology_proc_ops = {
>  	.proc_release	= single_release,
>  };
> 
> +int cpu_to_coregroup_id(int cpu)
> +{
> +	return cpu_to_core_id(cpu);
> +}


So, if has_coregroup_support() returns true, then since the core_group
identification is currently done through the core-id, the
coregroup_mask is going to be the same as the
cpu_core_mask/cpu_cpu_mask. Thus, we will be degenerating the DIE
domain. Right ? Instead we could have kept the core-group to be a
single bigcore by default, so that those domains can get degenerated
preserving the legacy SMT, DIE, NUMA hierarchy.




> +
>  static int topology_update_init(void)
>  {
>  	start_topology_update();
> -- 
> 2.17.1
>