Add metrics for beacon block propagation (#2173)

## Issue Addressed

NA

## Proposed Changes

Adds some metrics to track delays regarding:

- LH processing of blocks
- delays receiving blocks from other nodes.

## Additional Info

NA

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -24,7 +24,8 @@ use crate::shuffling_cache::{BlockShufflingIds, ShufflingCache};
 use crate::snapshot_cache::SnapshotCache;
 use crate::timeout_rw_lock::TimeoutRwLock;
 use crate::validator_monitor::{
-    ValidatorMonitor, HISTORIC_EPOCHS as VALIDATOR_MONITOR_HISTORIC_EPOCHS,
+    get_block_delay_ms, timestamp_now, ValidatorMonitor,
+    HISTORIC_EPOCHS as VALIDATOR_MONITOR_HISTORIC_EPOCHS,
 };
 use crate::validator_pubkey_cache::ValidatorPubkeyCache;
 use crate::BeaconForkChoiceStore;
@@ -1712,6 +1713,15 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         // This prevents inconsistency between the two at the expense of concurrency.
         drop(fork_choice);
 
+        // Log metrics to track the delay between when the block was made and when we imported it.
+        //
+        // We're declaring the block "imported" at this point, since fork choice and the DB know
+        // about it.
+        metrics::observe_duration(
+            &metrics::BEACON_BLOCK_IMPORTED_SLOT_START_DELAY_TIME,
+            get_block_delay_ms(timestamp_now(), &signed_block.message, &self.slot_clock),
+        );
+
         let parent_root = block.parent_root;
         let slot = block.slot;
 

beacon_node/beacon_chain/src/metrics.rs

@@ -570,6 +570,13 @@ lazy_static! {
         &["src", "validator"]
     );
 
+    /*
+     * Block Delay Metrics
+     */
+    pub static ref BEACON_BLOCK_IMPORTED_SLOT_START_DELAY_TIME: Result<Histogram> = try_create_histogram(
+        "beacon_block_imported_slot_start_delay_time",
+        "Duration between the start of the blocks slot and the current time.",
+    );
 }
 
 /// Scrape the `beacon_chain` for metrics that are not constantly updated (e.g., the present slot,

beacon_node/beacon_chain/src/validator_monitor.rs

@@ -367,18 +367,6 @@ impl<T: EthSpec> ValidatorMonitor<T> {
         }
     }
 
-    /// Returns the delay between the start of `block.slot` and `seen_timestamp`.
-    fn get_block_delay_ms<S: SlotClock>(
-        seen_timestamp: Duration,
-        block: &BeaconBlock<T>,
-        slot_clock: &S,
-    ) -> Duration {
-        slot_clock
-            .start_of(block.slot)
-            .and_then(|slot_start| seen_timestamp.checked_sub(slot_start))
-            .unwrap_or_else(|| Duration::from_secs(0))
-    }
-
     /// Process a block received on gossip.
     pub fn register_gossip_block<S: SlotClock>(
         &self,
@@ -410,7 +398,7 @@ impl<T: EthSpec> ValidatorMonitor<T> {
         slot_clock: &S,
     ) {
         if let Some(id) = self.get_validator_id(block.proposer_index) {
-            let delay = Self::get_block_delay_ms(seen_timestamp, block, slot_clock);
+            let delay = get_block_delay_ms(seen_timestamp, block, slot_clock);
 
             metrics::inc_counter_vec(&metrics::VALIDATOR_MONITOR_BEACON_BLOCK_TOTAL, &[src, id]);
             metrics::observe_timer_vec(
@@ -951,3 +939,15 @@ pub fn timestamp_now() -> Duration {
 fn u64_to_i64(n: impl Into<u64>) -> i64 {
     i64::try_from(n.into()).unwrap_or(i64::max_value())
 }
+
+/// Returns the delay between the start of `block.slot` and `seen_timestamp`.
+pub fn get_block_delay_ms<T: EthSpec, S: SlotClock>(
+    seen_timestamp: Duration,
+    block: &BeaconBlock<T>,
+    slot_clock: &S,
+) -> Duration {
+    slot_clock
+        .start_of(block.slot)
+        .and_then(|slot_start| seen_timestamp.checked_sub(slot_start))
+        .unwrap_or_else(|| Duration::from_secs(0))
+}