rpc: add a metric for the gas used on eth_call

Author: MqllR

internal/ethapi/api.go

@@ -775,6 +775,13 @@ func (api *BlockChainAPI) Call(ctx context.Context, args TransactionArgs, blockN
 	if err != nil {
 		return nil, err
 	}
+
+	if result.UsedGas > gomath.MaxInt64 {
+		rpcEthCallGasUsedHist.Update(gomath.MaxInt64)
+	} else {
+		rpcEthCallGasUsedHist.Update(int64(result.UsedGas))
+	}
+
 	if errors.Is(result.Err, vm.ErrExecutionReverted) {
 		return nil, newRevertError(result.Revert())
 	}

internal/ethapi/metrics.go

@@ -0,0 +1,21 @@
+// Copyright 2025 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package ethapi
+
+import "github.com/ethereum/go-ethereum/metrics"
+
+var rpcEthCallGasUsedHist = metrics.NewRegisteredHistogram("rpc/gas_used/eth_call", nil, metrics.NewExpDecaySample(1028, 0.015))