[RFC PATCH v3 03/10] sched: Static key to check paravirt cpu push

[Shrikanth Hegde <sshegde@linux.ibm.com>]

CPUs are marked paravirt when there is contention for underlying
physical CPU.

The push mechanism and check for paravirt CPUs are in sched tick
and wakeup. It should be close to no-op when there is no need for it.
Achieve that using static key.

Architecture needs to enable this key when it decides there are
paravirt CPUs. Disable it when there are no paravirt CPUs.

Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
 kernel/sched/core.c  |  1 +
 kernel/sched/sched.h | 17 +++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0f1e36bb5779..b8a84e4691c8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -10967,4 +10967,5 @@ void sched_enq_and_set_task(struct sched_enq_and_set_ctx *ctx)
 #ifdef CONFIG_PARAVIRT
 struct cpumask __cpu_paravirt_mask __read_mostly;
 EXPORT_SYMBOL(__cpu_paravirt_mask);
+DEFINE_STATIC_KEY_FALSE(cpu_paravirt_push_tasks);
 #endif
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index b5367c514c14..8f9991453d36 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -3880,4 +3880,21 @@ void sched_enq_and_set_task(struct sched_enq_and_set_ctx *ctx);
 
 #include "ext.h"
 
+#ifdef CONFIG_PARAVIRT
+DECLARE_STATIC_KEY_FALSE(cpu_paravirt_push_tasks);
+
+static inline bool is_cpu_paravirt(int cpu)
+{
+	if (static_branch_unlikely(&cpu_paravirt_push_tasks))
+		return cpu_paravirt(cpu);
+
+	return false;
+}
+#else	/* !CONFIG_PARAVIRT */
+static inline bool is_cpu_paravirt(int cpu)
+{
+	return false;
+}
+#endif	/* !CONFIG_PARAVIRT */
+
 #endif /* _KERNEL_SCHED_SCHED_H */
-- 
2.47.3