From 1f9b69b36d51988305de791d50d5422b5cc01ca6 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?P=C3=A9ter=20Szil=C3=A1gyi?= Date: Wed, 31 May 2023 10:21:13 +0300 Subject: [PATCH] consensus, core, eth/downloader, params: 4844 chain validation (#27382) --- consensus/beacon/consensus.go | 13 +++++--- consensus/clique/clique.go | 2 +- consensus/ethash/consensus.go | 2 +- consensus/misc/eip1559.go | 4 +-- consensus/misc/eip1559_test.go | 2 +- consensus/misc/eip4844.go | 56 ++++++++++++++++++++++++++++++---- consensus/misc/eip4844_test.go | 41 +++++++++++++++++++++---- core/block_validator.go | 17 +++++++++-- core/types/block.go | 47 ++++++++++++++++++++-------- core/types/gen_header_json.go | 50 +++++++++++++++++------------- core/types/gen_header_rlp.go | 21 ++++++++----- eth/downloader/queue.go | 16 ++++++++++ params/protocol_params.go | 2 ++ 13 files changed, 208 insertions(+), 65 deletions(-) diff --git a/consensus/beacon/consensus.go b/consensus/beacon/consensus.go index 75f1b65efa..c5d2a12a7b 100644 --- a/consensus/beacon/consensus.go +++ b/consensus/beacon/consensus.go @@ -257,7 +257,7 @@ func (beacon *Beacon) verifyHeader(chain consensus.ChainHeaderReader, header, pa return consensus.ErrInvalidNumber } // Verify the header's EIP-1559 attributes. - if err := misc.VerifyEip1559Header(chain.Config(), parent, header); err != nil { + if err := misc.VerifyEIP1559Header(chain.Config(), parent, header); err != nil { return err } // Verify existence / non-existence of withdrawalsHash. @@ -270,12 +270,17 @@ func (beacon *Beacon) verifyHeader(chain consensus.ChainHeaderReader, header, pa } // Verify the existence / non-existence of excessDataGas cancun := chain.Config().IsCancun(header.Number, header.Time) - if cancun && header.ExcessDataGas == nil { - return errors.New("missing excessDataGas") - } if !cancun && header.ExcessDataGas != nil { return fmt.Errorf("invalid excessDataGas: have %d, expected nil", header.ExcessDataGas) } + if !cancun && header.DataGasUsed != nil { + return fmt.Errorf("invalid dataGasUsed: have %d, expected nil", header.DataGasUsed) + } + if cancun { + if err := misc.VerifyEIP4844Header(parent, header); err != nil { + return err + } + } return nil } diff --git a/consensus/clique/clique.go b/consensus/clique/clique.go index dd35e9d28b..ee18820631 100644 --- a/consensus/clique/clique.go +++ b/consensus/clique/clique.go @@ -343,7 +343,7 @@ func (c *Clique) verifyCascadingFields(chain consensus.ChainHeaderReader, header if err := misc.VerifyGaslimit(parent.GasLimit, header.GasLimit); err != nil { return err } - } else if err := misc.VerifyEip1559Header(chain.Config(), parent, header); err != nil { + } else if err := misc.VerifyEIP1559Header(chain.Config(), parent, header); err != nil { // Verify the header's EIP-1559 attributes. return err } diff --git a/consensus/ethash/consensus.go b/consensus/ethash/consensus.go index acbbdacc3c..ad36f21ca9 100644 --- a/consensus/ethash/consensus.go +++ b/consensus/ethash/consensus.go @@ -254,7 +254,7 @@ func (ethash *Ethash) verifyHeader(chain consensus.ChainHeaderReader, header, pa if err := misc.VerifyGaslimit(parent.GasLimit, header.GasLimit); err != nil { return err } - } else if err := misc.VerifyEip1559Header(chain.Config(), parent, header); err != nil { + } else if err := misc.VerifyEIP1559Header(chain.Config(), parent, header); err != nil { // Verify the header's EIP-1559 attributes. return err } diff --git a/consensus/misc/eip1559.go b/consensus/misc/eip1559.go index fbaf9eec76..2697f029e2 100644 --- a/consensus/misc/eip1559.go +++ b/consensus/misc/eip1559.go @@ -27,10 +27,10 @@ import ( "github.com/ethereum/go-ethereum/params" ) -// VerifyEip1559Header verifies some header attributes which were changed in EIP-1559, +// VerifyEIP1559Header verifies some header attributes which were changed in EIP-1559, // - gas limit check // - basefee check -func VerifyEip1559Header(config *params.ChainConfig, parent, header *types.Header) error { +func VerifyEIP1559Header(config *params.ChainConfig, parent, header *types.Header) error { // Verify that the gas limit remains within allowed bounds parentGasLimit := parent.GasLimit if !config.IsLondon(parent.Number) { diff --git a/consensus/misc/eip1559_test.go b/consensus/misc/eip1559_test.go index 1a9f96bc43..59fded2cde 100644 --- a/consensus/misc/eip1559_test.go +++ b/consensus/misc/eip1559_test.go @@ -95,7 +95,7 @@ func TestBlockGasLimits(t *testing.T) { BaseFee: initial, Number: big.NewInt(tc.pNum + 1), } - err := VerifyEip1559Header(config(), parent, header) + err := VerifyEIP1559Header(config(), parent, header) if tc.ok && err != nil { t.Errorf("test %d: Expected valid header: %s", i, err) } diff --git a/consensus/misc/eip4844.go b/consensus/misc/eip4844.go index 66ca9bd26d..f370e49017 100644 --- a/consensus/misc/eip4844.go +++ b/consensus/misc/eip4844.go @@ -17,8 +17,11 @@ package misc import ( + "errors" + "fmt" "math/big" + "github.com/ethereum/go-ethereum/core/types" "github.com/ethereum/go-ethereum/params" ) @@ -27,13 +30,54 @@ var ( dataGaspriceUpdateFraction = big.NewInt(params.BlobTxDataGaspriceUpdateFraction) ) -// CalcBlobFee calculates the blobfee from the header's excess data gas field. -func CalcBlobFee(excessDataGas *big.Int) *big.Int { - // If this block does not yet have EIP-4844 enabled, return the starting fee - if excessDataGas == nil { - return big.NewInt(params.BlobTxMinDataGasprice) +// VerifyEIP4844Header verifies the presence of the excessDataGas field and that +// if the current block contains no transactions, the excessDataGas is updated +// accordingly. +func VerifyEIP4844Header(parent, header *types.Header) error { + // Verify the header is not malformed + if header.ExcessDataGas == nil { + return errors.New("header is missing excessDataGas") } - return fakeExponential(minDataGasPrice, excessDataGas, dataGaspriceUpdateFraction) + if header.DataGasUsed == nil { + return errors.New("header is missing dataGasUsed") + } + // Verify that the data gas used remains within reasonable limits. + if *header.DataGasUsed > params.BlobTxMaxDataGasPerBlock { + return fmt.Errorf("data gas used %d exceeds maximum allowance %d", *header.DataGasUsed, params.BlobTxMaxDataGasPerBlock) + } + if *header.DataGasUsed%params.BlobTxDataGasPerBlob != 0 { + return fmt.Errorf("data gas used %d not a multiple of data gas per blob %d", header.DataGasUsed, params.BlobTxDataGasPerBlob) + } + // Verify the excessDataGas is correct based on the parent header + var ( + parentExcessDataGas uint64 + parentDataGasUsed uint64 + ) + if parent.ExcessDataGas != nil { + parentExcessDataGas = *parent.ExcessDataGas + parentDataGasUsed = *parent.DataGasUsed + } + expectedExcessDataGas := CalcExcessDataGas(parentExcessDataGas, parentDataGasUsed) + if *header.ExcessDataGas != expectedExcessDataGas { + return fmt.Errorf("invalid excessDataGas: have %d, want %d, parent excessDataGas %d, parent blobDataUsed %d", + *header.ExcessDataGas, expectedExcessDataGas, parentExcessDataGas, parentDataGasUsed) + } + return nil +} + +// CalcExcessDataGas calculates the excess data gas after applying the set of +// blobs on top of the excess data gas. +func CalcExcessDataGas(parentExcessDataGas uint64, parentDataGasUsed uint64) uint64 { + excessDataGas := parentExcessDataGas + parentDataGasUsed + if excessDataGas < params.BlobTxTargetDataGasPerBlock { + return 0 + } + return excessDataGas - params.BlobTxTargetDataGasPerBlock +} + +// CalcBlobFee calculates the blobfee from the header's excess data gas field. +func CalcBlobFee(excessDataGas uint64) *big.Int { + return fakeExponential(minDataGasPrice, new(big.Int).SetUint64(excessDataGas), dataGaspriceUpdateFraction) } // fakeExponential approximates factor * e ** (numerator / denominator) using diff --git a/consensus/misc/eip4844_test.go b/consensus/misc/eip4844_test.go index 5838cab8e6..939ca25870 100644 --- a/consensus/misc/eip4844_test.go +++ b/consensus/misc/eip4844_test.go @@ -24,9 +24,42 @@ import ( "github.com/ethereum/go-ethereum/params" ) +func TestCalcExcessDataGas(t *testing.T) { + var tests = []struct { + excess uint64 + blobs uint64 + want uint64 + }{ + // The excess data gas should not increase from zero if the used blob + // slots are below - or equal - to the target. + {0, 0, 0}, + {0, 1, 0}, + {0, params.BlobTxTargetDataGasPerBlock / params.BlobTxDataGasPerBlob, 0}, + + // If the target data gas is exceeded, the excessDataGas should increase + // by however much it was overshot + {0, (params.BlobTxTargetDataGasPerBlock / params.BlobTxDataGasPerBlob) + 1, params.BlobTxDataGasPerBlob}, + {1, (params.BlobTxTargetDataGasPerBlock / params.BlobTxDataGasPerBlob) + 1, params.BlobTxDataGasPerBlob + 1}, + {1, (params.BlobTxTargetDataGasPerBlock / params.BlobTxDataGasPerBlob) + 2, 2*params.BlobTxDataGasPerBlob + 1}, + + // The excess data gas should decrease by however much the target was + // under-shot, capped at zero. + {params.BlobTxTargetDataGasPerBlock, params.BlobTxTargetDataGasPerBlock / params.BlobTxDataGasPerBlob, params.BlobTxTargetDataGasPerBlock}, + {params.BlobTxTargetDataGasPerBlock, (params.BlobTxTargetDataGasPerBlock / params.BlobTxDataGasPerBlob) - 1, params.BlobTxDataGasPerBlob}, + {params.BlobTxTargetDataGasPerBlock, (params.BlobTxTargetDataGasPerBlock / params.BlobTxDataGasPerBlob) - 2, 0}, + {params.BlobTxDataGasPerBlob - 1, (params.BlobTxTargetDataGasPerBlock / params.BlobTxDataGasPerBlob) - 1, 0}, + } + for _, tt := range tests { + result := CalcExcessDataGas(tt.excess, tt.blobs*params.BlobTxDataGasPerBlob) + if result != tt.want { + t.Errorf("excess data gas mismatch: have %v, want %v", result, tt.want) + } + } +} + func TestCalcBlobFee(t *testing.T) { tests := []struct { - excessDataGas int64 + excessDataGas uint64 blobfee int64 }{ {0, 1}, @@ -34,12 +67,8 @@ func TestCalcBlobFee(t *testing.T) { {1542707, 2}, {10 * 1024 * 1024, 111}, } - have := CalcBlobFee(nil) - if have.Int64() != params.BlobTxMinDataGasprice { - t.Errorf("nil test: blobfee mismatch: have %v, want %v", have, params.BlobTxMinDataGasprice) - } for i, tt := range tests { - have := CalcBlobFee(big.NewInt(tt.excessDataGas)) + have := CalcBlobFee(tt.excessDataGas) if have.Int64() != tt.blobfee { t.Errorf("test %d: blobfee mismatch: have %v want %v", i, have, tt.blobfee) } diff --git a/core/block_validator.go b/core/block_validator.go index fbd0d4bcf9..ce3e6560ee 100644 --- a/core/block_validator.go +++ b/core/block_validator.go @@ -78,10 +78,23 @@ func (v *BlockValidator) ValidateBody(block *types.Block) error { return fmt.Errorf("withdrawals root hash mismatch (header value %x, calculated %x)", *header.WithdrawalsHash, hash) } } else if block.Withdrawals() != nil { - // Withdrawals are not allowed prior to shanghai fork + // Withdrawals are not allowed prior to Shanghai fork return errors.New("withdrawals present in block body") } - + // Blob transactions may be present after the Cancun fork. + var blobs int + for _, tx := range block.Transactions() { + blobs += len(tx.BlobHashes()) + } + if header.DataGasUsed != nil { + if want := *header.DataGasUsed / params.BlobTxDataGasPerBlob; uint64(blobs) != want { // div because the header is surely good vs the body might be bloated + return fmt.Errorf("data gas used mismatch (header %v, calculated %v)", *header.DataGasUsed, blobs*params.BlobTxDataGasPerBlob) + } + } else { + if blobs > 0 { + return errors.New("data blobs present in block body") + } + } if !v.bc.HasBlockAndState(block.ParentHash(), block.NumberU64()-1) { if !v.bc.HasBlock(block.ParentHash(), block.NumberU64()-1) { return consensus.ErrUnknownAncestor diff --git a/core/types/block.go b/core/types/block.go index 58ea81676a..e1f1feb7a2 100644 --- a/core/types/block.go +++ b/core/types/block.go @@ -86,19 +86,24 @@ type Header struct { WithdrawalsHash *common.Hash `json:"withdrawalsRoot" rlp:"optional"` // ExcessDataGas was added by EIP-4844 and is ignored in legacy headers. - ExcessDataGas *big.Int `json:"excessDataGas" rlp:"optional"` + ExcessDataGas *uint64 `json:"excessDataGas" rlp:"optional"` + + // DataGasUsed was added by EIP-4844 and is ignored in legacy headers. + DataGasUsed *uint64 `json:"dataGasUsed" rlp:"optional"` } // field type overrides for gencodec type headerMarshaling struct { - Difficulty *hexutil.Big - Number *hexutil.Big - GasLimit hexutil.Uint64 - GasUsed hexutil.Uint64 - Time hexutil.Uint64 - Extra hexutil.Bytes - BaseFee *hexutil.Big - Hash common.Hash `json:"hash"` // adds call to Hash() in MarshalJSON + Difficulty *hexutil.Big + Number *hexutil.Big + GasLimit hexutil.Uint64 + GasUsed hexutil.Uint64 + Time hexutil.Uint64 + Extra hexutil.Bytes + BaseFee *hexutil.Big + Hash common.Hash `json:"hash"` // adds call to Hash() in MarshalJSON + ExcessDataGas *hexutil.Uint64 + DataGasUsed *hexutil.Uint64 } // Hash returns the block hash of the header, which is simply the keccak256 hash of its @@ -146,10 +151,10 @@ func (h *Header) SanityCheck() error { // EmptyBody returns true if there is no additional 'body' to complete the header // that is: no transactions, no uncles and no withdrawals. func (h *Header) EmptyBody() bool { - if h.WithdrawalsHash == nil { - return h.TxHash == EmptyTxsHash && h.UncleHash == EmptyUncleHash + if h.WithdrawalsHash != nil { + return h.TxHash == EmptyTxsHash && *h.WithdrawalsHash == EmptyWithdrawalsHash } - return h.TxHash == EmptyTxsHash && h.UncleHash == EmptyUncleHash && *h.WithdrawalsHash == EmptyWithdrawalsHash + return h.TxHash == EmptyTxsHash && h.UncleHash == EmptyUncleHash } // EmptyReceipts returns true if there are no receipts for this header/block. @@ -347,6 +352,24 @@ func (b *Block) Withdrawals() Withdrawals { return b.withdrawals } +func (b *Block) ExcessDataGas() *uint64 { + var excessDataGas *uint64 + if b.header.ExcessDataGas != nil { + excessDataGas = new(uint64) + *excessDataGas = *b.header.ExcessDataGas + } + return excessDataGas +} + +func (b *Block) DataGasUsed() *uint64 { + var dataGasUsed *uint64 + if b.header.DataGasUsed != nil { + dataGasUsed = new(uint64) + *dataGasUsed = *b.header.DataGasUsed + } + return dataGasUsed +} + func (b *Block) Header() *Header { return CopyHeader(b.header) } // Body returns the non-header content of the block. diff --git a/core/types/gen_header_json.go b/core/types/gen_header_json.go index 73287257bd..fe246d54ec 100644 --- a/core/types/gen_header_json.go +++ b/core/types/gen_header_json.go @@ -16,25 +16,26 @@ var _ = (*headerMarshaling)(nil) // MarshalJSON marshals as JSON. func (h Header) MarshalJSON() ([]byte, error) { type Header struct { - ParentHash common.Hash `json:"parentHash" gencodec:"required"` - UncleHash common.Hash `json:"sha3Uncles" gencodec:"required"` - Coinbase common.Address `json:"miner"` - Root common.Hash `json:"stateRoot" gencodec:"required"` - TxHash common.Hash `json:"transactionsRoot" gencodec:"required"` - ReceiptHash common.Hash `json:"receiptsRoot" gencodec:"required"` - Bloom Bloom `json:"logsBloom" gencodec:"required"` - Difficulty *hexutil.Big `json:"difficulty" gencodec:"required"` - Number *hexutil.Big `json:"number" gencodec:"required"` - GasLimit hexutil.Uint64 `json:"gasLimit" gencodec:"required"` - GasUsed hexutil.Uint64 `json:"gasUsed" gencodec:"required"` - Time hexutil.Uint64 `json:"timestamp" gencodec:"required"` - Extra hexutil.Bytes `json:"extraData" gencodec:"required"` - MixDigest common.Hash `json:"mixHash"` - Nonce BlockNonce `json:"nonce"` - BaseFee *hexutil.Big `json:"baseFeePerGas" rlp:"optional"` - WithdrawalsHash *common.Hash `json:"withdrawalsRoot" rlp:"optional"` - ExcessDataGas *big.Int `json:"excessDataGas" rlp:"optional"` - Hash common.Hash `json:"hash"` + ParentHash common.Hash `json:"parentHash" gencodec:"required"` + UncleHash common.Hash `json:"sha3Uncles" gencodec:"required"` + Coinbase common.Address `json:"miner"` + Root common.Hash `json:"stateRoot" gencodec:"required"` + TxHash common.Hash `json:"transactionsRoot" gencodec:"required"` + ReceiptHash common.Hash `json:"receiptsRoot" gencodec:"required"` + Bloom Bloom `json:"logsBloom" gencodec:"required"` + Difficulty *hexutil.Big `json:"difficulty" gencodec:"required"` + Number *hexutil.Big `json:"number" gencodec:"required"` + GasLimit hexutil.Uint64 `json:"gasLimit" gencodec:"required"` + GasUsed hexutil.Uint64 `json:"gasUsed" gencodec:"required"` + Time hexutil.Uint64 `json:"timestamp" gencodec:"required"` + Extra hexutil.Bytes `json:"extraData" gencodec:"required"` + MixDigest common.Hash `json:"mixHash"` + Nonce BlockNonce `json:"nonce"` + BaseFee *hexutil.Big `json:"baseFeePerGas" rlp:"optional"` + WithdrawalsHash *common.Hash `json:"withdrawalsRoot" rlp:"optional"` + ExcessDataGas *hexutil.Uint64 `json:"excessDataGas" rlp:"optional"` + DataGasUsed *hexutil.Uint64 `json:"dataGasUsed" rlp:"optional"` + Hash common.Hash `json:"hash"` } var enc Header enc.ParentHash = h.ParentHash @@ -54,7 +55,8 @@ func (h Header) MarshalJSON() ([]byte, error) { enc.Nonce = h.Nonce enc.BaseFee = (*hexutil.Big)(h.BaseFee) enc.WithdrawalsHash = h.WithdrawalsHash - enc.ExcessDataGas = h.ExcessDataGas + enc.ExcessDataGas = (*hexutil.Uint64)(h.ExcessDataGas) + enc.DataGasUsed = (*hexutil.Uint64)(h.DataGasUsed) enc.Hash = h.Hash() return json.Marshal(&enc) } @@ -79,7 +81,8 @@ func (h *Header) UnmarshalJSON(input []byte) error { Nonce *BlockNonce `json:"nonce"` BaseFee *hexutil.Big `json:"baseFeePerGas" rlp:"optional"` WithdrawalsHash *common.Hash `json:"withdrawalsRoot" rlp:"optional"` - ExcessDataGas *big.Int `json:"excessDataGas" rlp:"optional"` + ExcessDataGas *hexutil.Uint64 `json:"excessDataGas" rlp:"optional"` + DataGasUsed *hexutil.Uint64 `json:"dataGasUsed" rlp:"optional"` } var dec Header if err := json.Unmarshal(input, &dec); err != nil { @@ -149,7 +152,10 @@ func (h *Header) UnmarshalJSON(input []byte) error { h.WithdrawalsHash = dec.WithdrawalsHash } if dec.ExcessDataGas != nil { - h.ExcessDataGas = dec.ExcessDataGas + h.ExcessDataGas = (*uint64)(dec.ExcessDataGas) + } + if dec.DataGasUsed != nil { + h.DataGasUsed = (*uint64)(dec.DataGasUsed) } return nil } diff --git a/core/types/gen_header_rlp.go b/core/types/gen_header_rlp.go index 005f6c2ad4..f488931f1f 100644 --- a/core/types/gen_header_rlp.go +++ b/core/types/gen_header_rlp.go @@ -43,7 +43,8 @@ func (obj *Header) EncodeRLP(_w io.Writer) error { _tmp1 := obj.BaseFee != nil _tmp2 := obj.WithdrawalsHash != nil _tmp3 := obj.ExcessDataGas != nil - if _tmp1 || _tmp2 || _tmp3 { + _tmp4 := obj.DataGasUsed != nil + if _tmp1 || _tmp2 || _tmp3 || _tmp4 { if obj.BaseFee == nil { w.Write(rlp.EmptyString) } else { @@ -53,21 +54,25 @@ func (obj *Header) EncodeRLP(_w io.Writer) error { w.WriteBigInt(obj.BaseFee) } } - if _tmp2 || _tmp3 { + if _tmp2 || _tmp3 || _tmp4 { if obj.WithdrawalsHash == nil { w.Write([]byte{0x80}) } else { w.WriteBytes(obj.WithdrawalsHash[:]) } } - if _tmp3 { + if _tmp3 || _tmp4 { if obj.ExcessDataGas == nil { - w.Write(rlp.EmptyString) + w.Write([]byte{0x80}) } else { - if obj.ExcessDataGas.Sign() == -1 { - return rlp.ErrNegativeBigInt - } - w.WriteBigInt(obj.ExcessDataGas) + w.WriteUint64((*obj.ExcessDataGas)) + } + } + if _tmp4 { + if obj.DataGasUsed == nil { + w.Write([]byte{0x80}) + } else { + w.WriteUint64((*obj.DataGasUsed)) } } w.ListEnd(_tmp0) diff --git a/eth/downloader/queue.go b/eth/downloader/queue.go index e9907297a0..0a00d48901 100644 --- a/eth/downloader/queue.go +++ b/eth/downloader/queue.go @@ -31,6 +31,7 @@ import ( "github.com/ethereum/go-ethereum/core/types" "github.com/ethereum/go-ethereum/log" "github.com/ethereum/go-ethereum/metrics" + "github.com/ethereum/go-ethereum/params" ) const ( @@ -796,6 +797,21 @@ func (q *queue) DeliverBodies(id string, txLists [][]*types.Transaction, txListH return errInvalidBody } } + // Blocks must have a number of blobs corresponding to the header gas usage, + // and zero before the Cancun hardfork + var blobs int + for _, tx := range txLists[index] { + blobs += len(tx.BlobHashes()) + } + if header.DataGasUsed != nil { + if want := *header.DataGasUsed / params.BlobTxDataGasPerBlob; uint64(blobs) != want { // div because the header is surely good vs the body might be bloated + return errInvalidBody + } + } else { + if blobs != 0 { + return errInvalidBody + } + } return nil } diff --git a/params/protocol_params.go b/params/protocol_params.go index 1fb258c1fc..5ddc13c63b 100644 --- a/params/protocol_params.go +++ b/params/protocol_params.go @@ -160,6 +160,8 @@ const ( RefundQuotient uint64 = 2 RefundQuotientEIP3529 uint64 = 5 + BlobTxMaxDataGasPerBlock = 1 << 19 // Maximum consumable data gas for data blobs per block + BlobTxTargetDataGasPerBlock = 1 << 18 // Target consumable data gas for data blobs per block (for 1559-like pricing) BlobTxDataGasPerBlob = 1 << 17 // Gas consumption of a single data blob (== blob byte size) BlobTxMinDataGasprice = 1 // Minimum gas price for data blobs BlobTxDataGaspriceUpdateFraction = 2225652 // Controls the maximum rate of change for data gas price