x86/intel_rdt: Introduce rdt_enable_key for scheduling

Introduce the usage of rdt_enable_key in sched_in code as a preparation
to add RDT monitoring support for sched_in.

Signed-off-by: Vikas Shivappa <vikas.shivappa@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: ravi.v.shankar@intel.com
Cc: tony.luck@intel.com
Cc: fenghua.yu@intel.com
Cc: peterz@infradead.org
Cc: eranian@google.com
Cc: vikas.shivappa@intel.com
Cc: ak@linux.intel.com
Cc: davidcc@google.com
Cc: reinette.chatre@intel.com
Link: http://lkml.kernel.org/r/1501017287-28083-24-git-send-email-vikas.shivappa@linux.intel.com

arch/x86/include/asm/intel_rdt_sched.h

@@ -27,10 +27,12 @@ struct intel_pqr_state {
 
 DECLARE_PER_CPU(struct intel_pqr_state, pqr_state);
 DECLARE_PER_CPU_READ_MOSTLY(struct intel_pqr_state, rdt_cpu_default);
+
+DECLARE_STATIC_KEY_FALSE(rdt_enable_key);
 DECLARE_STATIC_KEY_FALSE(rdt_alloc_enable_key);
 
 /*
- * intel_rdt_sched_in() - Writes the task's CLOSid to IA32_PQR_MSR
+ * __intel_rdt_sched_in() - Writes the task's CLOSid to IA32_PQR_MSR
  *
  * Following considerations are made so that this has minimal impact
  * on scheduler hot path:
@@ -42,7 +44,7 @@ DECLARE_STATIC_KEY_FALSE(rdt_alloc_enable_key);
  *
  * Must be called with preemption disabled.
  */
-static inline void intel_rdt_sched_in(void)
+static inline void __intel_rdt_sched_in(void)
 {
 	if (static_branch_likely(&rdt_alloc_enable_key)) {
 		struct intel_pqr_state *state = this_cpu_ptr(&pqr_state);
@@ -63,6 +65,12 @@ static inline void intel_rdt_sched_in(void)
 	}
 }
 
+static inline void intel_rdt_sched_in(void)
+{
+	if (static_branch_likely(&rdt_enable_key))
+		__intel_rdt_sched_in();
+}
+
 #else
 
 static inline void intel_rdt_sched_in(void) {}