From 5880414319aef75aa746a1138dede8115be3320f Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Sat, 4 Dec 2021 10:14:02 +0100
Subject: [PATCH] sched,x86: Don't use cluster topology for x86 hybrid CPUs

References: jsc#SLE-18889,bnc#1194825
Patch-mainline: v5.16
Git-commit: cabdc3a8475b918e55744f43719b26a82dc8fa6b

For x86 hybrid CPUs like Alder Lake, the order of CPU selection should
be based strictly on CPU priority.  Don't include cluster topology for
hybrid CPUs to avoid interference with such CPU selection order.

On Alder Lake, the Atom CPU cluster has more capacity (4 Atom CPUs) vs
Big core cluster (2 hyperthread CPUs). This could potentially bias CPU
selection towards Atom over Big Core, when Big core CPU has higher
priority.

Fixes: 66558b730f25 ("sched: Add cluster scheduler level for x86")
Suggested-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Tim Chen <tim.c.chen@linux.intel.com>
Tested-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Link: https://lkml.kernel.org/r/20211204091402.GM16608@worktop.programming.kicks-ass.net
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 arch/x86/kernel/smpboot.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 29107089f2e9..65f0a83eed0f 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -579,6 +579,17 @@ static struct sched_domain_topology_level x86_numa_in_package_topology[] = {
 	{ NULL, },
 };
 
+static struct sched_domain_topology_level x86_hybrid_topology[] = {
+#ifdef CONFIG_SCHED_SMT
+	{ cpu_smt_mask, x86_smt_flags, SD_INIT_NAME(SMT) },
+#endif
+#ifdef CONFIG_SCHED_MC
+	{ cpu_coregroup_mask, x86_core_flags, SD_INIT_NAME(MC) },
+#endif
+	{ cpu_cpu_mask, SD_INIT_NAME(DIE) },
+	{ NULL, },
+};
+
 static struct sched_domain_topology_level x86_topology[] = {
 #ifdef CONFIG_SCHED_SMT
 	{ cpu_smt_mask, x86_smt_flags, SD_INIT_NAME(SMT) },
@@ -1466,8 +1477,11 @@ void __init native_smp_cpus_done(unsigned int max_cpus)
 
 	calculate_max_logical_packages();
 
+	/* XXX for now assume numa-in-package and hybrid don't overlap */
 	if (x86_has_numa_in_package)
 		set_sched_topology(x86_numa_in_package_topology);
+	if (cpu_feature_enabled(X86_FEATURE_HYBRID_CPU))
+		set_sched_topology(x86_hybrid_topology);
 
 	nmi_selftest();
 	impress_friends();