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I propose a small experiment to see if this trivial (and recognized as correct) change makes a noticeable difference. I leave to QA the win threshold which requires inclusion in 1.5 or 1.6.

The change is here and in the attachment too.

diff --git a/src/lib/dhcp/packet_queue_ring.h b/src/lib/dhcp/packet_queue_ring.h
index 315e2a0375..bcaa496747 100644
--- a/src/lib/dhcp/packet_queue_ring.h
+++ b/src/lib/dhcp/packet_queue_ring.h
@@ -123,12 +123,12 @@ public:
     /// @return A pointer to dequeued packet, or an empty pointer
     /// if the queue is empty.
     virtual PacketTypePtr popPacket(const QueueEnd& from = QueueEnd::FRONT) {
-        isc::util::thread::Mutex::Locker lock(mutex_);
         PacketTypePtr packet;
         if (queue_.empty()) {
             return (packet);
         }
 
+        isc::util::thread::Mutex::Locker lock(mutex_);
         if (from == QueueEnd::FRONT) {
             packet = queue_.front();
             queue_.pop_front();

better-lock.diff