sched: Add new API wake_up_if_idle() to wake up the idle cpu

Implementing one new API wake_up_if_idle(), which is used to
wake up the idle CPU.

Suggested-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Chuansheng Liu <chuansheng.liu@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: daniel.lezcano@linaro.org
Cc: rjw@rjwysocki.net
Cc: linux-pm@vger.kernel.org
Cc: changcheng.liu@intel.com
Cc: xiaoming.wang@intel.com
Cc: souvik.k.chakravarty@intel.com
Cc: chuansheng.liu@intel.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1409815075-4180-1-git-send-email-chuansheng.liu@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 20 insertions, 0 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index dd9eb4807389..82ff3d6efb19 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1024,6 +1024,7 @@ struct sched_domain_topology_level {
 extern struct sched_domain_topology_level *sched_domain_topology;
 
 extern void set_sched_topology(struct sched_domain_topology_level *tl);
+extern void wake_up_if_idle(int cpu);
 
 #ifdef CONFIG_SCHED_DEBUG
 # define SD_INIT_NAME(type)             .name = #type
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 78e5c839df13..f7c6ed2fd69d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1634,6 +1634,25 @@ static void ttwu_queue_remote(struct task_struct *p, int cpu)
         }
 }
 
+void wake_up_if_idle(int cpu)
+{
+        struct rq *rq = cpu_rq(cpu);
+        unsigned long flags;
+
+        if (!is_idle_task(rq->curr))
+                return;
+
+        if (set_nr_if_polling(rq->idle)) {
+                trace_sched_wake_idle_without_ipi(cpu);
+        } else {
+                raw_spin_lock_irqsave(&rq->lock, flags);
+                if (is_idle_task(rq->curr))
+                        smp_send_reschedule(cpu);
+                /* Else cpu is not in idle, do nothing here */
+                raw_spin_unlock_irqrestore(&rq->lock, flags);
+        }
+}
+
 bool cpus_share_cache(int this_cpu, int that_cpu)
 {
         return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);