Subject: [PATCH v5 06/10] powerpc/smp: Optimize start_secondary

From: Srikar Dronamraju <[email-masked]>
Date: Mon, 10 Aug 2020 12:48:30 +0530

In start_secondary, even if shared_cache was already set, system does a
redundant match for cpumask. This redundant check can be removed by
checking if shared_cache is already set.

While here, localize the sibling_mask variable to within the if
condition.

Cc: linuxppc-dev <[email-masked]>
Cc: LKML <[email-masked]>
Cc: Michael Ellerman <[email-masked]>
Cc: Nicholas Piggin <[email-masked]>
Cc: Anton Blanchard <[email-masked]>
Cc: Oliver O'Halloran <[email-masked]>
Cc: Nathan Lynch <[email-masked]>
Cc: Michael Neuling <[email-masked]>
Cc: Gautham R Shenoy <[email-masked]>
Cc: Ingo Molnar <[email-masked]>
Cc: Peter Zijlstra <[email-masked]>
Cc: Valentin Schneider <[email-masked]>
Cc: Jordan Niethe <[email-masked]>
Cc: Vaidyanathan Srinivasan <[email-masked]>
Signed-off-by: Srikar Dronamraju <[email-masked]>
---
Changelog v4 ->v5:
	Retain cache domain, no need for generalization
		 (Michael Ellerman, Peter Zijlstra,
		 Valentin Schneider, Gautham R. Shenoy)

Changelog v1 -> v2:
	Moved shared_cache topology fixup to fixup_topology (Gautham)

 arch/powerpc/kernel/smp.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 0c960ce3be42..91cf5d05e7ec 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -851,7 +851,7 @@ static int powerpc_shared_cache_flags(void)
  */
 static const struct cpumask *shared_cache_mask(int cpu)
 {
-	return cpu_l2_cache_mask(cpu);
+	return per_cpu(cpu_l2_cache_map, cpu);
 }
 
 #ifdef CONFIG_SCHED_SMT
@@ -1305,7 +1305,6 @@ static void add_cpu_to_masks(int cpu)
 void start_secondary(void *unused)
 {
 	unsigned int cpu = smp_processor_id();
-	struct cpumask *(*sibling_mask)(int) = cpu_sibling_mask;
 
 	mmgrab(&init_mm);
 	current->active_mm = &init_mm;
@@ -1331,14 +1330,20 @@ void start_secondary(void *unused)
 	/* Update topology CPU masks */
 	add_cpu_to_masks(cpu);
 
-	if (has_big_cores)
-		sibling_mask = cpu_smallcore_mask;
 	/*
 	 * Check for any shared caches. Note that this must be done on a
 	 * per-core basis because one core in the pair might be disabled.
 	 */
-	if (!cpumask_equal(cpu_l2_cache_mask(cpu), sibling_mask(cpu)))
-		shared_caches = true;
+	if (!shared_caches) {
+		struct cpumask *(*sibling_mask)(int) = cpu_sibling_mask;
+		struct cpumask *mask = cpu_l2_cache_mask(cpu);
+
+		if (has_big_cores)
+			sibling_mask = cpu_smallcore_mask;
+
+		if (cpumask_weight(mask) > cpumask_weight(sibling_mask(cpu)))
+			shared_caches = true;
+	}
 
 	set_numa_node(numa_cpu_lookup_table[cpu]);
 	set_numa_mem(local_memory_node(numa_cpu_lookup_table[cpu]));
-- 
2.18.2