On 08/03/2022 12:04, Vincent Guittot wrote: > On Tue, 8 Mar 2022 at 11:30, Will Deacon <will@xxxxxxxxxx> wrote: [...] >>> --- >>> v1: Drop MC level if coregroup weight == 1 >>> v2: New sd topo in arch/arm64/kernel/smp.c >>> v3: No new topo, extend core_mask to cluster_siblings >>> >>> drivers/base/arch_topology.c | 8 ++++++++ >>> 1 file changed, 8 insertions(+) >>> >>> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c >>> index 976154140f0b..a96f45db928b 100644 >>> --- a/drivers/base/arch_topology.c >>> +++ b/drivers/base/arch_topology.c >>> @@ -628,6 +628,14 @@ const struct cpumask *cpu_coregroup_mask(int cpu) >>> core_mask = &cpu_topology[cpu].llc_sibling; >>> } >>> >>> + /* >>> + * For systems with no shared cpu-side LLC but with clusters defined, >>> + * extend core_mask to cluster_siblings. The sched domain builder will >>> + * then remove MC as redundant with CLS if SCHED_CLUSTER is enabled. IMHO, if core_mask weight is 1, MC will be removed/degenerated anyway. This is what I get on my Ampere Altra (I guess I don't have the ACPI changes which would let to a CLS sched domain): # cat /sys/kernel/debug/sched/domains/cpu0/domain*/name DIE NUMA root@oss-altra01:~# zcat /proc/config.gz | grep SCHED_CLUSTER CONFIG_SCHED_CLUSTER=y >>> + */ >>> + if (cpumask_subset(core_mask, &cpu_topology[cpu].cluster_sibling)) >>> + core_mask = &cpu_topology[cpu].cluster_sibling; >>> + >> >> Sudeep, Vincent, are you happy with this now? > > I would not say that I'm happy because this solution skews the core > cpu mask in order to abuse the scheduler so that it will remove a > wrong but useless level when it will build its domains. > But this works so as long as the maintainer are happy, I'm fine I do not have any better idea than this tweak here either in case the platform can't provide a cleaner setup. Maybe the following is easier to read but then we use '&cpu_topology[cpu].llc_sibling' in cpu_coregroup_mask() already ... @@ -617,6 +617,7 @@ EXPORT_SYMBOL_GPL(cpu_topology); const struct cpumask *cpu_coregroup_mask(int cpu) { const cpumask_t *core_mask = cpumask_of_node(cpu_to_node(cpu)); + const cpumask_t *cluster_mask = cpu_clustergroup_mask(cpu); /* Find the smaller of NUMA, core or LLC siblings */ if (cpumask_subset(&cpu_topology[cpu].core_sibling, core_mask)) { @@ -628,6 +629,9 @@ const struct cpumask *cpu_coregroup_mask(int cpu) core_mask = &cpu_topology[cpu].llc_sibling; } + if (cpumask_subset(core_mask, cluster_mask)) + core_mask = cluster_mask; + return core_mask; } Reviewed-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>