Changes to improve performance

The work queue processing was causing too much overhead so a more
efficient check was implemented.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/modules/uORB/uORBDevices_posix.cpp

@@ -287,6 +287,7 @@ uORB::DeviceNode::ioctl(device::file_t *filp, int cmd, unsigned long arg)
 
 	case ORBIOCSETINTERVAL:
 		sd->update_interval = arg;
+		sd->last_update = hrt_absolute_time();
 		return PX4_OK;
 
 	case ORBIOCGADVERTISER:
@@ -426,31 +427,17 @@ uORB::DeviceNode::appears_updated(SubscriberData *sd)
 			break;
 		}
 
-		/*
-		 * If the interval timer is still running, the topic should not
-		 * appear updated, even though at this point we know that it has.
-		 * We have previously been through here, so the subscriber
-		 * must have collected the update we reported, otherwise
-		 * update_reported would still be true.
-		 */
-		if (!hrt_called(&sd->update_call)) {
+		// If we have not yet reached the deadline, then assume that we can ignore any
+		// newly received data.
+		if (sd->last_update + sd->update_interval > hrt_absolute_time()) {
 			break;
 		}
 
-		/*
-		 * Make sure that we don't consider the topic to be updated again
-		 * until the interval has passed once more by restarting the interval
-		 * timer and thereby re-scheduling a poll notification at that time.
-		 */
-		hrt_call_after(&sd->update_call,
-			       sd->update_interval,
-			       &uORB::DeviceNode::update_deferred_trampoline,
-			       (void *)this);
-
 		/*
 		 * Remember that we have told the subscriber that there is data.
 		 */
 		sd->update_reported = true;
+		sd->last_update = hrt_absolute_time();
 		ret = true;
 
 		break;