[PATCH v2 6/6] powerpc/smp: Avoid asym packing within thread_group of a core

Srikar Dronamraju
2023-10-18T16:40:50Z

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@linux.vnet.ibm.com>
---
arch/powerpc/kernel/smp.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index b1eb11a66902..a710fb32a2a9 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -1695,6 +1695,8 @@ void start_secondary(void *unused)
BUG();
}

+DEFINE_STATIC_KEY_FALSE(splpar_asym_pack);
+
static void __init fixup_topology(void)
{
int i;
@@ -1704,6 +1706,7 @@ static void __init fixup_topology(void)
static_branch_enable(&powerpc_asym_packing);
} else if (is_shared_processor() && has_big_cores) {
static_branch_enable(&powerpc_asym_packing);
+ static_branch_enable(&splpar_asym_pack);
}

#ifdef CONFIG_SCHED_SMT
@@ -1758,6 +1761,19 @@ 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