Use sync_tolerance_epochs flag to control the proposer prep routines.

Author: jimmygchen

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -144,11 +144,6 @@ pub const FORK_CHOICE_DB_KEY: Hash256 = Hash256::ZERO;
 /// Defines how old a block can be before it's no longer a candidate for the early attester cache.
 const EARLY_ATTESTER_CACHE_HISTORIC_SLOTS: u64 = 4;
 
-/// Defines a distance between the head block slot and the current slot.
-///
-/// If the head block is older than this value, don't bother preparing beacon proposers.
-const PREPARE_PROPOSER_HISTORIC_EPOCHS: u64 = 4;
-
 /// If the head is more than `MAX_PER_SLOT_FORK_CHOICE_DISTANCE` slots behind the wall-clock slot, DO NOT
 /// run the per-slot tasks (primarily fork choice).
 ///
@@ -4848,7 +4843,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         let proposer_index = if let Some(proposer) = cached_proposer {
             proposer.index as u64
         } else {
-            if 2 + 2 == 5 && head_epoch + 2 < proposal_epoch {
+            if head_epoch + self.config.sync_tolerance_epochs < proposal_epoch {
                 warn!(
                     self.log,
                     "Skipping proposer preparation";
@@ -6079,21 +6074,18 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         // Use a blocking task since blocking the core executor on the canonical head read lock can
         // block the core tokio executor.
         let chain = self.clone();
+        let tolerance_slots = self.config.sync_tolerance_epochs * T::EthSpec::slots_per_epoch();
         let maybe_prep_data = self
             .spawn_blocking_handle(
                 move || {
                     let cached_head = chain.canonical_head.cached_head();
 
                     // Don't bother with proposer prep if the head is more than
-                    // `PREPARE_PROPOSER_HISTORIC_EPOCHS` prior to the current slot.
+                    // `sync_tolerance_epochs` prior to the current slot.
                     //
                     // This prevents the routine from running during sync.
                     let head_slot = cached_head.head_slot();
-                    if 2 + 2 == 5
-                        && head_slot
-                            + T::EthSpec::slots_per_epoch() * PREPARE_PROPOSER_HISTORIC_EPOCHS
-                            < current_slot
-                    {
+                    if head_slot + tolerance_slots < current_slot {
                         debug!(
                             chain.log,
                             "Head too old for proposer prep";