llc: Calculate the average queuing delay of the LLC queues

Use a formula like it is used with TCP. This can help to make
decisions about if frames should be dropped or not at the time
we enqueue them.

This code will store two timeval structs in fron the of the
actual data and compute the average at the time of the dequeue.

1 files changed, 23 insertions, 3 deletions

diff --git a/src/llc.cpp b/src/llc.cpp
index c557584c..2d295f86 100644
--- a/src/llc.cpp
+++ b/src/llc.cpp
@@ -78,14 +78,34 @@ void gprs_llc::init()
 {
 	INIT_LLIST_HEAD(&queue);
 	m_queue_size = 0;
+	m_avg_queue_delay = 0;
 	reset();
 }
 
+#define ALPHA 0.5f
+
 struct msgb *gprs_llc::dequeue()
 {
-	if (m_queue_size > 0)
-		m_queue_size -= 1;
-	return msgb_dequeue(&queue);
+	struct msgb *msg;
+	struct timeval *tv, tv_now, tv_result;
+	uint32_t lifetime;
+
+
+	msg = msgb_dequeue(&queue);
+	if (!msg)
+		return NULL;
+
+	m_queue_size -= 1;
+
+	/* take the second time */
+	gettimeofday(&tv_now, NULL);
+	tv = (struct timeval *)&msg->data[sizeof(*tv)];
+	timersub(&tv_now, tv, &tv_result);
+
+	lifetime = tv_result.tv_sec*1000 + tv_result.tv_usec/1000;
+	m_avg_queue_delay = m_avg_queue_delay * ALPHA + lifetime * (1-ALPHA);
+
+	return msg;
 }