From 80e5fb58f99a121765ee4799bfdb95ec45e72412 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bart=C5=82omiej=20Kami=C5=84ski?= <bart@casperlabs.io>
Date: Thu, 31 Oct 2024 14:16:28 +0100
Subject: [PATCH] Avoid iterating through all rounds when determining
 participation

---
 .../src/components/consensus/protocols/zug.rs | 16 ++++++++----
 .../consensus/protocols/zug/participation.rs  | 25 +++++++++++--------
 2 files changed, 25 insertions(+), 16 deletions(-)

diff --git a/node/src/components/consensus/protocols/zug.rs b/node/src/components/consensus/protocols/zug.rs
index 121169410b..7c81b488e4 100644
--- a/node/src/components/consensus/protocols/zug.rs
+++ b/node/src/components/consensus/protocols/zug.rs
@@ -1523,12 +1523,18 @@ impl<C: Context + 'static> Zug<C> {
     /// Adds a signed message content to the state.
     /// Does not call `update` and does not detect faults.
     fn add_content(&mut self, signed_msg: SignedMessage<C>) -> bool {
-        if self.active[signed_msg.validator_idx].is_none() {
+        if self.active[signed_msg.validator_idx]
+            .as_ref()
+            .map_or(true, |old_msg| old_msg.round_id < signed_msg.round_id)
+        {
+            if self.active[signed_msg.validator_idx].is_none() {
+                // We considered this validator inactive until now, and didn't accept proposals that
+                // didn't have them in the `inactive` field. Mark all relevant rounds as dirty so
+                // that the next `update` call checks all proposals again.
+                self.mark_dirty(self.first_non_finalized_round_id);
+            }
+            // Save the latest signed message for participation tracking purposes.
             self.active[signed_msg.validator_idx] = Some(signed_msg.clone());
-            // We considered this validator inactive until now, and didn't accept proposals that
-            // didn't have them in the `inactive` field. Mark all relevant rounds as dirty so that
-            // the next `update` call checks all proposals again.
-            self.mark_dirty(self.first_non_finalized_round_id);
         }
         let SignedMessage {
             round_id,
diff --git a/node/src/components/consensus/protocols/zug/participation.rs b/node/src/components/consensus/protocols/zug/participation.rs
index 4ca1b22d78..f91435a17c 100644
--- a/node/src/components/consensus/protocols/zug/participation.rs
+++ b/node/src/components/consensus/protocols/zug/participation.rs
@@ -42,18 +42,21 @@ impl ParticipationStatus {
                 Fault::Direct(..) => ParticipationStatus::Equivocated,
             });
         }
-        // TODO: Avoid iterating over all old rounds every time we log this.
-        for r_id in zug.rounds.keys().rev() {
-            if zug.has_echoed(*r_id, idx)
-                || zug.has_voted(*r_id, idx)
-                || (zug.has_accepted_proposal(*r_id) && zug.leader(*r_id) == idx)
-            {
-                if r_id.saturating_add(2) < zug.current_round {
-                    return Some(ParticipationStatus::LastSeenInRound(*r_id));
-                }
-                return None; // Seen recently; considered currently active.
+
+        let last_seen_round = zug
+            .active
+            .get(idx)
+            .and_then(Option::as_ref)
+            .map(|signed_msg| signed_msg.round_id);
+        match last_seen_round {
+            // not seen at all
+            None => Some(ParticipationStatus::Inactive),
+            // seen, but not within last 2 rounds
+            Some(r_id) if r_id.saturating_add(2) < zug.current_round => {
+                Some(ParticipationStatus::LastSeenInRound(r_id))
             }
+            // seen recently
+            _ => None,
         }
-        Some(ParticipationStatus::Inactive)
     }
 }