[RFCv3 5/8] powerpc: Define Core Capacity for POWER systems

[Parth Shah]

This patch tunes arch_scale_core_capacity for powerpc arch by scaling
capacity w.r.t to the number of online SMT in the core such that for SMT-4,
core capacity is 1.5x the capacity of sibling thread.

Signed-off-by: Parth Shah <parth@xxxxxxxxxxxxx>
---
 arch/powerpc/include/asm/topology.h |  4 ++++
 arch/powerpc/kernel/smp.c           | 33 +++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h
index f85e2b01c3df..1c777ee67180 100644
--- a/arch/powerpc/include/asm/topology.h
+++ b/arch/powerpc/include/asm/topology.h
@@ -132,6 +132,10 @@ static inline void shared_proc_topology_init(void) {}
 #define topology_sibling_cpumask(cpu)	(per_cpu(cpu_sibling_map, cpu))
 #define topology_core_cpumask(cpu)	(per_cpu(cpu_core_map, cpu))
 #define topology_core_id(cpu)		(cpu_to_core_id(cpu))
+#define arch_scale_core_capacity	powerpc_scale_core_capacity
+
+unsigned long powerpc_scale_core_capacity(int first_smt,
+					  unsigned long smt_cap);
 
 int dlpar_cpu_readd(int cpu);
 #endif
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index ea6adbf6a221..149a3fbf8ed3 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -1169,6 +1169,39 @@ static void remove_cpu_from_masks(int cpu)
 }
 #endif
 
+#ifdef CONFIG_SCHED_SMT
+/*
+ * Calculate capacity of a core based on the active threads in the core
+ * Scale the capacity of first SM-thread based on total number of
+ * active threads in the respective smt_mask.
+ *
+ * The scaling is done such that for
+ * SMT-4, core_capacity = 1.5x first_cpu_capacity
+ * and for SMT-8, core_capacity multiplication factor is 2x
+ *
+ * So, core_capacity multiplication factor = (1 + smt_mode*0.125)
+ *
+ * @first_cpu: First/any CPU id in the core
+ * @cap: Capacity of the first_cpu
+ */
+unsigned long powerpc_scale_core_capacity(int first_cpu,
+					  unsigned long cap)
+{
+	struct cpumask select_idles;
+	struct cpumask *cpus = &select_idles;
+	int cpu, smt_mode = 0;
+
+	cpumask_and(cpus, cpu_smt_mask(first_cpu), cpu_online_mask);
+
+	/* Find SMT mode from active SM-threads */
+	for_each_cpu(cpu, cpus)
+		smt_mode++;
+
+	/* Scale core capacity based on smt mode */
+	return smt_mode == 1 ? cap : ((cap * smt_mode) >> 3) + cap;
+}
+#endif
+
 static inline void add_cpu_to_smallcore_masks(int cpu)
 {
 	struct cpumask *this_l1_cache_map = per_cpu(cpu_l1_cache_map, cpu);
-- 
2.17.1