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

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Message-ID: <20230830105244.62477-4-srikar@linux.vnet.ibm.com>
Date:   Wed, 30 Aug 2023 16:22:43 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Juergen Gross <jgross@...e.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Paul E McKenney <paulmck@...nel.org>,
        Valentin Schneider <vschneid@...hat.com>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 3/4] powerpc/smp: Enable Asym packing for cores on shared processor

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 <srikar@...ux.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