feat(engine): add metric for forkchoiceUpdated response -> newPayload (#21380)

crates/engine/tree/src/tree/metrics.rs

@@ -254,6 +254,8 @@ pub(crate) struct NewPayloadStatusMetrics {
     pub(crate) time_between_new_payloads: Histogram,
     /// Time from previous payload start to current payload start (total interval).
     pub(crate) new_payload_interval: Histogram,
+    /// Time diff between forkchoice updated call response and the next new payload call request.
+    pub(crate) forkchoice_updated_new_payload_time_diff: Histogram,
 }
 
 impl NewPayloadStatusMetrics {
@@ -261,6 +263,7 @@ impl NewPayloadStatusMetrics {
     pub(crate) fn update_response_metrics(
         &mut self,
         start: Instant,
+        latest_forkchoice_updated_at: &mut Option<Instant>,
         result: &Result<TreeOutcome<PayloadStatus>, InsertBlockFatalError>,
         gas_used: u64,
     ) {
@@ -293,6 +296,10 @@ impl NewPayloadStatusMetrics {
         self.new_payload_messages.increment(1);
         self.new_payload_latency.record(elapsed);
         self.new_payload_last.set(elapsed);
+        if let Some(latest_forkchoice_updated_at) = latest_forkchoice_updated_at.take() {
+            self.forkchoice_updated_new_payload_time_diff
+                .record(start - latest_forkchoice_updated_at);
+        }
     }
 }
 

crates/engine/tree/src/tree/mod.rs

@@ -1514,10 +1514,12 @@ where
                                 let gas_used = payload.gas_used();
                                 let num_hash = payload.num_hash();
                                 let mut output = self.on_new_payload(payload);
-                                self.metrics
-                                    .engine
-                                    .new_payload
-                                    .update_response_metrics(start, &output, gas_used);
+                                self.metrics.engine.new_payload.update_response_metrics(
+                                    start,
+                                    &mut self.metrics.engine.forkchoice_updated.latest_finish_at,
+                                    &output,
+                                    gas_used,
+                                );
 
                                 let maybe_event =
                                     output.as_mut().ok().and_then(|out| out.event.take());