From 1b568f0aabf280555125bc7cefc08321ff0ebaba Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Mon, 9 May 2016 10:38:41 +0200
Subject: sched/core: Optimize SCHED_SMT

Avoid pointless SCHED_SMT code when running on !SMT hardware.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/core.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

(limited to 'kernel/sched/core.c')

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 75ecd4f29199..94115453c1c4 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7412,6 +7412,22 @@ int sched_cpu_dying(unsigned int cpu)
 }
 #endif
 
+#ifdef CONFIG_SCHED_SMT
+DEFINE_STATIC_KEY_FALSE(sched_smt_present);
+
+static void sched_init_smt(void)
+{
+	/*
+	 * We've enumerated all CPUs and will assume that if any CPU
+	 * has SMT siblings, CPU0 will too.
+	 */
+	if (cpumask_weight(cpu_smt_mask(0)) > 1)
+		static_branch_enable(&sched_smt_present);
+}
+#else
+static inline void sched_init_smt(void) { }
+#endif
+
 void __init sched_init_smp(void)
 {
 	cpumask_var_t non_isolated_cpus;
@@ -7441,6 +7457,9 @@ void __init sched_init_smp(void)
 
 	init_sched_rt_class();
 	init_sched_dl_class();
+
+	sched_init_smt();
+
 	sched_smp_initialized = true;
 }
 
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