allow for biasing comparisons between engine/builder api bids (#4847)

beacon_chain/conf.nim

@@ -587,6 +587,13 @@ type
         defaultValue: ""
         name: "payload-builder-url" .}: string
 
+      # Flag name and semantics borrowed from Prysm
+      # https://github.com/prysmaticlabs/prysm/pull/12227/files
+      localBlockValueBoost* {.
+        desc: "Increase execution layer block values for builder bid comparison by a percentage"
+        defaultValue: 0
+        name: "local-block-value-boost" .}: uint8
+
       historyMode* {.
         desc: "Retention strategy for historical data (archive/prune)"
         defaultValue: HistoryMode.Archive

beacon_chain/validators/validator_duties.nim

@@ -821,7 +821,8 @@ proc proposeBlockAux(
     SBBB: typedesc, EPS: typedesc, node: BeaconNode,
     validator: AttachedValidator, validator_index: ValidatorIndex,
     head: BlockRef, slot: Slot, randao: ValidatorSig, fork: Fork,
-    genesis_validators_root: Eth2Digest): Future[BlockRef] {.async.} =
+    genesis_validators_root: Eth2Digest,
+    localBlockValueBoost: uint8): Future[BlockRef] {.async.} =
   # Collect bids
   let usePayloadBuilder =
     if node.config.payloadBuilderEnable:
@@ -887,10 +888,24 @@ proc proposeBlockAux(
         err = engineBlockFut.error.msg
       false
 
+  template builderBetterBid(builderValue: UInt256, engineValue: Wei): bool =
+    # Scale down to ensure no overflows; if lower few bits would have been
+    # otherwise decisive, was close enough not to matter. Calibrate to let
+    # uint8-range percentages avoid overflowing.
+    const scalingBits = 10
+    static: doAssert 1 shl scalingBits >
+      high(typeof(localBlockValueBoost)).uint16 + 100
+    let
+      scaledBuilderValue = (builderValue shr scalingBits) * 100
+      scaledEngineValue = engineValue shr scalingBits
+    scaledBuilderValue >
+      scaledEngineValue * (localBlockValueBoost.uint16 + 100).u256
+
   let useBuilderBlock =
     if builderBidAvailable:
-      (not engineBidAvailable) or payloadBuilderBidFut.read.get().blockValue >
-        engineBlockFut.read.get().blockValue
+      (not engineBidAvailable) or builderBetterBid(
+        payloadBuilderBidFut.read.get().blockValue,
+        engineBlockFut.read.get().blockValue)
     else:
       if not engineBidAvailable:
         return head   # errors logged in router
@@ -1018,7 +1033,7 @@ proc proposeBlock(node: BeaconNode,
   template proposeBlockContinuation(type1, type2: untyped): auto =
     await proposeBlockAux(
       type1, type2, node, validator, validator_index, head, slot, randao, fork,
-        genesis_validators_root)
+        genesis_validators_root, node.config.localBlockValueBoost)
 
   return
     if slot.epoch >= node.dag.cfg.DENEB_FORK_EPOCH:

docs/the_nimbus_book/src/options.md

@@ -120,6 +120,8 @@ The following options are available:
      --suggested-gas-limit     Suggested gas limit [=defaultGasLimit].
      --payload-builder         Enable external payload builder [=false].
      --payload-builder-url     Payload builder URL.
+     --local-block-value-boost  Increase execution layer block values for builder bid comparison by a percentage
+                               [=0].
      --history                 Retention strategy for historical data (archive/prune) [=HistoryMode.Archive].
 
 ...