sched: add cpu isolation support

This adds cpu isolation APIs to the scheduler to isolate and unisolate
CPUs. Isolating and unisolating a CPU can be used in place of hotplug.
Isolating and unisolating a CPU is faster than hotplug and can thus be
used to optimize the performance and power of multi-core CPUs.

Isolating works by migrating non-pinned IRQs and tasks to other CPUS and
marking the CPU as not available to the scheduler and load balancer.
Pinned tasks and IRQs are still allowed to run but it is expected that
this would be minimal.

Unisolation works by just marking the CPU available for scheduler and
load balancer.

Change-Id: I0bbddb56238c2958c5987877c5bfc3e79afa67cc
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>

1 files changed, 35 insertions, 0 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index ac6b519494a2..a395d8a9ff73 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -363,6 +363,41 @@ extern cpumask_var_t cpu_isolated_map;
 
 extern int runqueue_is_locked(int cpu);
 
+#ifdef CONFIG_HOTPLUG_CPU
+extern int sched_isolate_count(const cpumask_t *mask, bool include_offline);
+extern int sched_isolate_cpu(int cpu);
+extern int sched_unisolate_cpu(int cpu);
+extern int sched_unisolate_cpu_unlocked(int cpu);
+#else
+static inline int sched_isolate_count(const cpumask_t *mask,
+				      bool include_offline)
+{
+	cpumask_t count_mask;
+
+	if (include_offline)
+		cpumask_andnot(&count_mask, mask, cpu_online_mask);
+	else
+		return 0;
+
+	return cpumask_weight(&count_mask);
+}
+
+static inline int sched_isolate_cpu(int cpu)
+{
+	return 0;
+}
+
+static inline int sched_unisolate_cpu(int cpu)
+{
+	return 0;
+}
+
+static inline int sched_unisolate_cpu_unlocked(int cpu)
+{
+	return 0;
+}
+#endif
+
 #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
 extern void nohz_balance_enter_idle(int cpu);
 extern void set_cpu_sd_state_idle(void);