CoDel seems to be incorrectly dropping packets

[Centaurus99]

In the CODELPacketQueue::dequeue function, dodequeue_result r is redefined at Line 74 and Line 84. Therefore, it seems that this function finally returns the packet obtained from dodequeue at line 65, which may have been intended to be dropped.

mahimahi/src/packet/codel_packet_queue.cc

Lines 62 to 94 in 0bd1216

	QueuedPacket CODELPacketQueue::dequeue( void )
	{
	const uint64_t now = timestamp();
	dodequeue_result r = std::move( dodequeue ( now ) );
	uint32_t delta;
	if ( dropping_ ) {
	if ( !r.ok_to_drop ) {
	dropping_ = false;
	}
	while ( now >= drop_next_ && dropping_ ) {
	dodequeue_result r = std::move( dodequeue ( now ) );
	count_++;
	if ( ! r.ok_to_drop ) {
	dropping_ = false;
	} else {
	drop_next_ = control_law(drop_next_, count_);
	}
	}
	}
	else if ( r.ok_to_drop ) {
	dodequeue_result r = std::move( dodequeue ( now ) );
	dropping_ = true;
	delta = count_ - lastcount_;
	count_ = ( ( delta > 1 ) && ( now - drop_next_ < 16 * interval_ ))?
	delta : 1;
	drop_next_ = control_law ( now, count_ );
	lastcount_ = count_;
	}
	return r.p;
	}

This does not seem to affect the number of dropped packets, but rather which specific packet is dropped.

If this is indeed a bug, perhaps this patch should work.

diff --git a/src/packet/codel_packet_queue.cc b/src/packet/codel_packet_queue.cc
index 047d2c1..d33b86e 100755
--- a/src/packet/codel_packet_queue.cc
+++ b/src/packet/codel_packet_queue.cc
@@ -71,7 +71,7 @@ QueuedPacket CODELPacketQueue::dequeue( void )
     }
 
     while ( now >= drop_next_ && dropping_ ) {
-      dodequeue_result r = std::move( dodequeue ( now ) );
+      r = std::move( dodequeue ( now ) );
       count_++;
       if ( ! r.ok_to_drop ) {
 	dropping_ = false;
@@ -81,7 +81,7 @@ QueuedPacket CODELPacketQueue::dequeue( void )
     }
   }
   else if ( r.ok_to_drop ) {
-    dodequeue_result r = std::move( dodequeue ( now ) );
+    r = std::move( dodequeue ( now ) );
     dropping_ = true;
     delta = count_ - lastcount_;
     count_ = ( ( delta > 1 ) && ( now - drop_next_ < 16 * interval_ ))?