[PATCH 3/4] powerpc/smp: Enable Asym packing for cores on shared processor

[Srikar Dronamraju]

If there are shared processor lpars, underlying Hypervisor can have more
virtual cores to handle that actual physical cores.

Starting with Power 9, a core has 2 nearly independent thread groups.
On a shared processors lpars, it helps to pack threads to lesser number
of cores so that the overall system performance and utilization
improves. PowerVM schedules at a core level. Hence packing to fewer
cores helps.

For example: Lets says there are two 8-core Shared lpars that are
actually sharing a 8 Core shared physical pool, each running 8 threads
each. Then Consolidating 8 threads to 4 cores on each lpar would help
them to perform better.

To achieve this, enable SD_ASYM_PACKING flag at CACHE, MC and DIE level.

Signed-off-by: Srikar Dronamraju <sri...@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/smp.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index c7d1484ed230..51403640440c 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -1005,7 +1005,12 @@ static int powerpc_smt_flags(void)
  */
 static int powerpc_shared_cache_flags(void)
 {
-       return SD_SHARE_PKG_RESOURCES;
+       return SD_SHARE_PKG_RESOURCES | asym_pack_flag;
+}
+
+static int powerpc_shared_proc_flags(void)
+{
+       return asym_pack_flag;
 }
 
 /*
@@ -1044,8 +1049,8 @@ static struct sched_domain_topology_level 
powerpc_topology[] = {
        { cpu_smt_mask, powerpc_smt_flags, SD_INIT_NAME(SMT) },
 #endif
        { shared_cache_mask, powerpc_shared_cache_flags, SD_INIT_NAME(CACHE) },
-       { cpu_mc_mask, SD_INIT_NAME(MC) },
-       { cpu_cpu_mask, SD_INIT_NAME(DIE) },
+       { cpu_mc_mask, powerpc_shared_proc_flags, SD_INIT_NAME(MC) },
+       { cpu_cpu_mask, powerpc_shared_proc_flags, SD_INIT_NAME(DIE) },
        { NULL, },
 };
 
@@ -1671,7 +1676,9 @@ static void __init fixup_topology(void)
 {
        int i;
 
-       if (cpu_has_feature(CPU_FTR_ASYM_SMT)) {
+       if (is_shared_processor()) {
+               asym_pack_flag = SD_ASYM_PACKING;
+       } else if (cpu_has_feature(CPU_FTR_ASYM_SMT)) {
                printk_once(KERN_INFO "Enabling Asymmetric SMT scheduling\n");
                asym_pack_flag = SD_ASYM_PACKING;
        }
-- 
2.41.0