Benchmark Ethereum Pallet (#149)

* Add skeleton for worst case import_unsigned_header

* Fix a typo

* Add benchmark test for best case unsigned header import

* Add finality verification to worst case bench

* Move `insert_header()` from mock to test_utils

Allows the benchmarking code to use this without having to pull it in from the mock.

* Add a rough bench to test a finalizing a "long" chain

* Try to use complexity parameter for finality bench

* Improve long finality bench

* Remove stray dot file

* Remove old "worst" case bench

* Scribble some ideas down for pruning bench

* Prune headers during benchmarking

* Clean up some comments

* Make finality bench work for entire range of complexity parameter

* Place initialization code into a function

* Add bench for block finalization with caching

* First attempt at bench with receipts

* Try and trigger validator set change

* Perform a validator set change during benchmarking

* Move `validators_change_receipt()` to shared location

Allows unit tests and benchmarks to access the same helper function
and const

* Extract a test receipt root into a constant

* Clean up description of pruning bench

* Fix cache and pruning tests

* Remove unecessary `build_custom_header` usage

* Get rid of warnings

* Remove code duplication comment

I don't think its entirely worth it to split out so few lines of code.
The benches aren't particularly hard to read anyways.

* Increase the range of the complexity parameter

* Use dynamic number of receipts while benchmarking

As part of this change we have removed the hardcoded TEST_RECEIPT_ROOT
and instead chose to calculate the receipt root on the fly. This will
make tests and benches less fragile.

* Prune a dynamic number of headers

bridges/modules/ethereum/src/test_utils.rs

@@ -21,12 +21,18 @@
 //!
 //! On the other hand, they may be used directly by the bechmarking module.
 
+// Since this is test code it's fine that not everything is used
+#![allow(dead_code)]
+
+use crate::finality::FinalityVotes;
+use crate::validators::CHANGE_EVENT_HASH;
 use crate::verification::calculate_score;
+use crate::{HeaderToImport, Storage};
 
 use primitives::{
 	rlp_encode,
 	signatures::{secret_to_address, sign, SignHeader},
-	Address, Bloom, Header, SealedEmptyStep, H256, U256,
+	Address, Bloom, Header, Receipt, SealedEmptyStep, H256, U256,
 };
 use secp256k1::SecretKey;
 use sp_std::prelude::*;
@@ -206,6 +212,39 @@ where
 	custom_header.sign_by(author)
 }
 
+/// Insert unverified header into storage.
+pub fn insert_header<S: Storage>(storage: &mut S, header: Header) {
+	storage.insert_header(HeaderToImport {
+		context: storage.import_context(None, &header.parent_hash).unwrap(),
+		is_best: true,
+		id: header.compute_id(),
+		header,
+		total_difficulty: 0.into(),
+		enacted_change: None,
+		scheduled_change: None,
+		finality_votes: FinalityVotes::default(),
+	});
+}
+
+pub fn validators_change_receipt(parent_hash: H256) -> Receipt {
+	use primitives::{LogEntry, TransactionOutcome};
+
+	Receipt {
+		gas_used: 0.into(),
+		log_bloom: (&[0xff; 256]).into(),
+		outcome: TransactionOutcome::Unknown,
+		logs: vec![LogEntry {
+			address: [3; 20].into(),
+			topics: vec![CHANGE_EVENT_HASH.into(), parent_hash],
+			data: vec![
+				0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+				0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 7, 7, 7, 7,
+				7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
+			],
+		}],
+	}
+}
+
 pub mod validator_utils {
 	use super::*;