[PATCH v4 4/5] powerpc/smp: Avoid asym packing within thread_group of a core

[Srikar Dronamraju]

PowerVM Hypervisor will schedule at a core granularity. However each
core can have more than one thread_groups. For better utilization in
case of a shared processor, its preferable for the scheduler to pack to
the lowest core. However there is no benefit of moving a thread between
two thread groups of the same core.

Signed-off-by: Srikar Dronamraju <srikar at linux.vnet.ibm.com>
---
 arch/powerpc/kernel/smp.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 65a6f988374a..a84931c37246 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -1763,6 +1763,19 @@ void __init smp_cpus_done(unsigned int max_cpus)
 	set_sched_topology(powerpc_topology);
 }
 
+/*
+ * For asym packing, by default lower numbered CPU has higher priority.
+ * On shared processors, pack to lower numbered core. However avoid moving
+ * between thread_groups within the same core.
+ */
+int arch_asym_cpu_priority(int cpu)
+{
+	if (static_branch_unlikely(&splpar_asym_pack))
+		return -cpu / threads_per_core;
+
+	return -cpu;
+}
+
 #ifdef CONFIG_HOTPLUG_CPU
 int __cpu_disable(void)
 {
-- 
2.31.1