Merge pull request #1015 from oasisprotocol/jberci/feature/gas-costs

Update gas costs

client-sdk/go/modules/contracts/types.go

@@ -300,12 +300,17 @@ type GasCosts struct {
 
 	SubcallDispatch uint64 `json:"subcall_dispatch"`
 
-	WASMStorageGetBase    uint64 `json:"wasm_storage_get_base"`
-	WASMStorageInsertBase uint64 `json:"wasm_storage_insert_base"`
-	WASMStorageRemoveBase uint64 `json:"wasm_storage_remove_base"`
-	WASMStorageKeyByte    uint64 `json:"wasm_storage_key_byte"`
-	WASMStorageValueByte  uint64 `json:"wasm_storage_value_byte"`
-	WASMEnvQueryBase      uint64 `json:"wasm_env_query_base"`
+	WASMPublicStorageGetBase          uint64 `json:"wasm_public_storage_get_base"`
+	WASMPublicStorageInsertBase       uint64 `json:"wasm_public_storage_insert_base"`
+	WASMPublicStorageRemoveBase       uint64 `json:"wasm_public_storage_remove_base"`
+	WASMPublicStorageKeyByte          uint64 `json:"wasm_public_storage_key_byte"`
+	WASMPublicStorageValueByte        uint64 `json:"wasm_public_storage_value_byte"`
+	WASMConfidentialStorageGetBase    uint64 `json:"wasm_confidential_storage_get_base"`
+	WASMConfidentialStorageInsertBase uint64 `json:"wasm_confidential_storage_insert_base"`
+	WASMConfidentialStorageRemoveBase uint64 `json:"wasm_confidential_storage_remove_base"`
+	WASMConfidentialStorageKeyByte    uint64 `json:"wasm_confidential_storage_key_byte"`
+	WASMConfidentialStorageValueByte  uint64 `json:"wasm_confidential_storage_value_byte"`
+	WASMEnvQueryBase                  uint64 `json:"wasm_env_query_base"`
 
 	WASMCryptoECDSARecover             uint64 `json:"wasm_crypto_ecdsa_recover"`
 	WASMCryptoSignatureVerifyEd25519   uint64 `json:"wasm_crypto_signature_verify_ed25519"`

runtime-sdk/modules/contracts/Cargo.toml

@@ -27,6 +27,11 @@ walrus = "0.19.0"
 
 [dev-dependencies]
 wat = "1.0"
+k256 = { version = "0.9.6", default-features = false, features = ["keccak256", "ecdsa"] }
+hex = "0.4.2"
+wasmprinter = "0.2.41"
+pretty_assertions = "1.3.0"
 
 [features]
 debug-utils = []
+benchmarks = [] # Enable inline benchmarks for use with `cargo bench`.

runtime-sdk/modules/contracts/README.md

@@ -0,0 +1,76 @@
+# Gas Cost Derivation
+
+The `wasm_*` gas cost defaults as defined in this crate are derived from
+the relative performance of various WASM instructions and the linked-in
+functions provided by the Runtime SDK.
+
+To replicate, start by running benchmarks from the top of the cargo
+workspace:
+
+    # To run all benchmarks:
+    $ cargo bench --features benchmarks -- --nocapture
+    # To run only the cost-related wasm benchmarks:
+    $ cargo bench --features benchmarks -p oasis-runtime-sdk-contracts -- --nocapture wasm
+
+The `--nocapture` flag to the test runner is needed due to the two
+single-run benchmarks (the signature verification compiled to WASM and
+the time waster test), which print some run statistics to stdout --
+these serve as a baseline for what is possible within a given amount of
+time.
+
+## Instruction Costs
+
+To determine the cost function for single instructions, examine the
+`bench_loop_*` statistics in the `wasm` module. `add` is one of the
+simplest instructions and is taken as a base for all other instructions;
+its cost is fixed to 1.
+
+The benchmarks are written such that they differ in as few instructions
+as possible. While not perfect, the relative performance should serve as
+a rule of thumb for how much gas/time their respective instructions
+cost. The `bench_loop_*_skel` tests show approximately how much time is
+taken by the skeleton of each type of benchmark -- the difference
+between these and the instruction-specific ones show how much a given
+sequence of instructions takes to execute.
+
+Note that the instruction benchmarks include repetition on two levels:
+the WASM code executes the main body in a loop, and the function call
+into WASM itself is repeated by the `Bencher` class.
+
+The total gas usage expected to be possible during computation for a
+single block can then be derived from the time waster benchmark, meant
+to run for roughly the time of one block. The amount of gas used for
+that benchmark gives an optimistic upper limit, since the instructions
+making it up are simple arithmetic, comparisons and calls (all
+relatively cheap instructions). An appropriate gas limit can be
+determined from it by applying some margin to allow for speed variations
+and other uncertainties as desired (for the defaults here, the
+assumption was to take a quarter of the measurement; half to approximate
+actual block time and another half as margin).
+
+## Operation Costs
+
+Based on the set gas usage limit per block and the expected real time
+available to the contract per block, check the storage and crypto
+benchmarks in the `abi::oasis` module.
+
+The crypto benchmarks provide an estimation of how much slower a
+WASM-native signature verification would be compared to the
+implementation provided by the SDK (`called_from_wasm_included` vs.
+`computed_in_wasm`) as well as how the SDK-provided functions compare to
+one another (the other benchmarks).
+
+Similarly, the storage benchmarks provide an estimation for how the
+three MKVS store operations perform relative to each other and how much
+the overhead is to call an operation from WASM (including copying bytes
+to and from instance memory).
+
+Regarding the difference between public and confidential storage, refer
+to the benchmarks in the `oasis_runtime_sdk` package, in the
+`storage::confidential` module.
+
+For guidance regarding per-byte costs for storage operations, see the
+storage waster benchmark
+(`abi::oasis::storage::test::bench_wasm_reach_gas_limit`). This tests
+how much storage can be used up in a single block given a set of
+default-constructed gas costs.