add more instrumentation for sending status back to sc (#614)

fix dispatche channel update by using replace instead of add

src/spu/src/controllers/leader_replica/replica_state.rs

@@ -256,7 +256,9 @@ where
     }
 
     pub async fn send_status_to_sc(&self, sc_sink: &SharedSinkMessageChannel) {
-        sc_sink.send(self.as_lrs_request()).await
+        let lrs = self.as_lrs_request();
+        debug!(hw = lrs.leader.hw, leo = lrs.leader.leo);
+        sc_sink.send(lrs).await
     }
 }
 

src/spu/src/controllers/sc/message_sink.rs

@@ -19,7 +19,7 @@ impl ScSinkMessageChannel {
     /// newer entry will overwrite previous if it has not been cleared
     pub async fn send(&self, request: LrsRequest) {
         let mut lock = self.0.lock().await;
-        lock.insert(request);
+        lock.replace(request);
     }
 
     pub async fn remove_all(&self) -> Vec<LrsRequest> {