Subject: [RFC PATCH 2/2] s390/topology: Add initial implementation for selection of parked CPUs

From: Tobias Huschle <[email-masked]>
Date: Wed, 4 Dec 2024 12:21:49 +0100

In this simplified example, vertical low CPUs are parked generally. 
This will later be adjusted by making the parked state dependent 
on the overall utilization on the underlying hypervisor.

Vertical lows are always bound to the highest CPU IDs. This implies that
the three types of vertically polarized CPUs are always clustered by ID.
This has the following implications:
- There can be scheduler domains consisting of only vertical highs
- There can be scheduler domains consisting of only vertical lows

Signed-off-by: Tobias Huschle <[email-masked]>
---
 arch/s390/include/asm/topology.h | 3 +++
 arch/s390/kernel/topology.c      | 5 +++++
 2 files changed, 8 insertions(+)

diff --git a/arch/s390/include/asm/topology.h b/arch/s390/include/asm/topology.h
index cef06bffad80..e86afeccde35 100644
--- a/arch/s390/include/asm/topology.h
+++ b/arch/s390/include/asm/topology.h
@@ -99,6 +99,9 @@ static inline int numa_node_id(void)
 
 #endif /* CONFIG_NUMA */
 
+#define arch_cpu_parked cpu_parked
+int cpu_parked(int cpu);
+
 #include <asm-generic/topology.h>
 
 #endif /* _ASM_S390_TOPOLOGY_H */
diff --git a/arch/s390/kernel/topology.c b/arch/s390/kernel/topology.c
index 4f9c301a705b..1032b65da574 100644
--- a/arch/s390/kernel/topology.c
+++ b/arch/s390/kernel/topology.c
@@ -299,6 +299,11 @@ void store_topology(struct sysinfo_15_1_x *info)
 	stsi(info, 15, 1, topology_mnest_limit());
 }
 
+int cpu_parked(int cpu)
+{
+	return smp_cpu_get_polarization(cpu) == POLARIZATION_VL;
+}
+
 static void __arch_update_dedicated_flag(void *arg)
 {
 	if (topology_cpu_dedicated(smp_processor_id()))
-- 
2.34.1