x86/sysctl: Add sysctl for ITMT scheduling feature

Intel Turbo Boost Max Technology 3.0 (ITMT) feature
allows some cores to be boosted to higher turbo
frequency than others.

Add /proc/sys/kernel/sched_itmt_enabled so operator
can enable/disable scheduling of tasks that favor cores
with higher turbo boost frequency potential.

By default, system that is ITMT capable and single
socket has this feature turned on.  It is more likely
to be lightly loaded and operates in Turbo range.

When there is a change in the ITMT scheduling operation
desired, a rebuild of the sched domain is initiated
so the scheduler can set up sched domains with appropriate
flag to enable/disable ITMT scheduling operations.

Co-developed-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Co-developed-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Cc: linux-pm@vger.kernel.org
Cc: peterz@infradead.org
Cc: jolsa@redhat.com
Cc: rjw@rjwysocki.net
Cc: linux-acpi@vger.kernel.org
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: bp@suse.de
Link: http://lkml.kernel.org/r/07cc62426a28bad57b01ab16bb903a9c84fa5421.1479844244.git.tim.c.chen@linux.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 5 insertions, 2 deletions

diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
index 8ace9511347c..4813df5c21f0 100644
--- a/arch/x86/include/asm/topology.h
+++ b/arch/x86/include/asm/topology.h
@@ -152,23 +152,26 @@ extern bool x86_topology_update;
 #include <asm/percpu.h>
 
 DECLARE_PER_CPU_READ_MOSTLY(int, sched_core_priority);
+extern unsigned int __read_mostly sysctl_sched_itmt_enabled;
 
 /* Interface to set priority of a cpu */
 void sched_set_itmt_core_prio(int prio, int core_cpu);
 
 /* Interface to notify scheduler that system supports ITMT */
-void sched_set_itmt_support(void);
+int sched_set_itmt_support(void);
 
 /* Interface to notify scheduler that system revokes ITMT support */
 void sched_clear_itmt_support(void);
 
 #else /* CONFIG_SCHED_ITMT */
 
+#define sysctl_sched_itmt_enabled	0
 static inline void sched_set_itmt_core_prio(int prio, int core_cpu)
 {
 }
-static inline void sched_set_itmt_support(void)
+static inline int sched_set_itmt_support(void)
 {
+	return 0;
 }
 static inline void sched_clear_itmt_support(void)
 {