[Sound-open-firmware] [PATCH] scheduler: check for any queued task before making context switch

[Liam Girdwood]

Minimise any context switches in the scheduler by first checking for
any queued tasks in the task list prior to changing context. If there are
no queued tasks then there is no need to context switch.

Signed-off-by: Liam Girdwood <liam.r.girdwood at linux.intel.com>
---
 src/lib/schedule.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/src/lib/schedule.c b/src/lib/schedule.c
index 1310e83..bfbb1b9 100644
--- a/src/lib/schedule.c
+++ b/src/lib/schedule.c
@@ -333,8 +333,31 @@ static void scheduler_run(void *unused)
 /* run the scheduler */
 void schedule(void)
 {
+	struct list_item *tlist;
+	struct task *task;
+	uint32_t flags;
+
 	tracev_pipe("sch");
 
+	spin_lock_irq(&sch->lock, flags);
+
+	/* make sure we have a queued task in the list first before we
+	   start scheduling as contexts switches are not free. */
+	list_for_item(tlist, &sch->list) {
+		task = container_of(tlist, struct task, list);
+
+		/* schedule if we find any queued tasks */
+		if (task->state == TASK_STATE_QUEUED) {
+			spin_unlock_irq(&sch->lock, flags);
+			goto schedule;
+		}
+	}
+
+	/* no task to schedule */
+	spin_unlock_irq(&sch->lock, flags);
+	return;
+
+schedule:
 	/* TODO: detect current IRQ context and call scheduler_run if both
 	 * current context matches scheduler context. saves a DSP context
 	 * switch.
-- 
2.11.0