On Tue, Mar 08, 2022 at 05:03:07PM +0100, Dietmar Eggemann wrote:
On 08/03/2022 12:04, Vincent Guittot wrote:
On Tue, 8 Mar 2022 at 11:30, Will Deacon will@kernel.org 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
I'd like to follow up on this. Would you share your dmidecode BIOS Information section?
Which kernel version?
*/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 did explore the other options and they added considerably more complexity without much benefit in my view. I prefer this option which maintains the cpu_topology as described by the platform, and maps it into something that suits the current scheduler abstraction. I agree there is more work to be done here and intend to continue with it.
I do not have any better idea than this tweak here either in case the platform can't provide a cleaner setup.
I'd argue The platform is describing itself accurately in ACPI PPTT terms. The topology doesn't fit nicely within the kernel abstractions today. This is an area where I hope to continue to improve things going forward.
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;
Either works for me. I felt the version I sent was parallel to the existing implementation, but have no preference either way.
return core_mask;}
Reviewed-by: Dietmar Eggemann dietmar.eggemann@arm.com
Thanks for the review Dietmar.