Proposer builds block in parallel. (Consensus vs Execution) (#12297)

* Proposer builds block in parallel. Cosensus vs Execution

* Update beacon-chain/rpc/prysm/v1alpha1/validator/proposer.go

Co-authored-by: Preston Van Loon <preston@prysmaticlabs.com>

* Use feature flag

---------

Co-authored-by: Preston Van Loon <preston@prysmaticlabs.com>

config/features/config.go

@@ -67,6 +67,8 @@ type Flags struct {
 
 	PrepareAllPayloads bool // PrepareAllPayloads informs the engine to prepare a block on every slot.
 
+	BuildBlockParallel bool // BuildBlockParallel builds beacon block for proposer in parallel.
+
 	// KeystoreImportDebounceInterval specifies the time duration the validator waits to reload new keys if they have
 	// changed on disk. This feature is for advanced use cases only.
 	KeystoreImportDebounceInterval time.Duration
@@ -212,6 +214,10 @@ func ConfigureBeaconChain(ctx *cli.Context) error {
 		logEnabled(prepareAllPayloads)
 		cfg.PrepareAllPayloads = true
 	}
+	if ctx.IsSet(buildBlockParallel.Name) {
+		logEnabled(buildBlockParallel)
+		cfg.BuildBlockParallel = true
+	}
 	Init(cfg)
 	return nil
 }

config/features/flags.go

@@ -118,6 +118,10 @@ var (
 		Name:  "prepare-all-payloads",
 		Usage: "Informs the engine to prepare all local payloads. Useful for relayers and builders",
 	}
+	buildBlockParallel = &cli.BoolFlag{
+		Name:  "build-block-parallel",
+		Usage: "Builds a beacon block in parallel for consensus and execution. It results in faster block construction time",
+	}
 )
 
 // devModeFlags holds list of flags that are set when development mode is on.
@@ -164,6 +168,7 @@ var BeaconChainFlags = append(deprecatedBeaconFlags, append(deprecatedFlags, []c
 	enableVerboseSigVerification,
 	enableOptionalEngineMethods,
 	prepareAllPayloads,
+	buildBlockParallel,
 }...)...)
 
 // E2EBeaconChainFlags contains a list of the beacon chain feature flags to be tested in E2E.