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perf: faster PoW guessing by precalculating MT auth paths
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Precalculate as much as possible towards the block hash such that only
the necessary hashing from updating a nonce is performed. Uses the
concept of Merkle authentication paths to achieve this. Also makes the
updates of some block header parameters stochastic to only happen on
average every 1m guesses.
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@Sword-Smith
Sword-Smith committed Jan 16, 2025
1 parent e491b2e commit 5c5650b
Showing 1 changed file with 85 additions and 58 deletions.
143 changes: 85 additions & 58 deletions src/mine_loop.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@ use std::time::Duration;
use anyhow::bail;
use anyhow::Result;
use block_header::BlockHeader;
use block_header::BlockHeaderField;
use block_header::MINIMUM_BLOCK_TIME;
use composer_parameters::ComposerParameters;
use difficulty_control::Difficulty;
Expand All @@ -19,7 +20,6 @@ use rayon::iter::ParallelIterator;
use rayon::ThreadPoolBuilder;
use tasm_lib::prelude::Tip5;
use tasm_lib::triton_vm::prelude::BFieldCodec;
use tasm_lib::twenty_first::prelude::MerkleTree;
use tokio::select;
use tokio::sync::mpsc;
use tokio::task::JoinHandle;
Expand Down Expand Up @@ -127,16 +127,33 @@ async fn guess_nonce(
.unwrap()
}

/// Return MAST leafs from which the block hash is calculated. Returns those
/// MAST leaves that can be precalculated prior to PoW-guessing.
/// Return MAST nodes from which the block header MAST hash is calculated,
/// given a variable nonce.
fn precalculate_header_ap(block_header_template: &BlockHeader) -> [Digest; 3] {
let header_mt = block_header_template.merkle_tree();

let nonce_auth_path = header_mt
.authentication_structure(&[BlockHeaderField::Nonce as usize])
.unwrap()
.try_into()
.unwrap();

nonce_auth_path
}

/// Return MAST nodes from which the block hash is calculated, given a
/// variable block header.
///
/// Returns (block body MAST hash digest, appendix digest)
fn precalculate_mast_leafs(block_template: &Block) -> (Digest, Digest) {
/// Returns those MAST nodes that can be precalculated prior to PoW-guessing.
/// This vastly reduces the amount of hashing needed for each PoW-guess.
fn precalculate_block_auth_paths(block_template: &Block) -> ([Digest; 2], [Digest; 3]) {
let block_body_mast_hash_digest =
Tip5::hash_varlen(&block_template.body().mast_hash().encode());
let appendix_digest = Tip5::hash_varlen(&block_template.appendix().encode());
let mt_node_3 = Tip5::hash_pair(appendix_digest, Digest::default());
let header_ap = precalculate_header_ap(block_template.header());

(block_body_mast_hash_digest, appendix_digest)
([block_body_mast_hash_digest, mt_node_3], header_ap)
}

fn guess_worker(
Expand Down Expand Up @@ -168,7 +185,7 @@ fn guess_worker(
// note: number of rayon threads can be set with env var RAYON_NUM_THREADS
// see: https://docs.rs/rayon/latest/rayon/fn.max_num_threads.html
let block_header_template = block.header().to_owned();
let (block_body_mast_hash_digest, appendix_digest) = precalculate_mast_leafs(&block);
let (kernel_auth_path, header_auth_path) = precalculate_block_auth_paths(&block);

let pool = ThreadPoolBuilder::new()
.num_threads(threads_to_use)
Expand All @@ -177,19 +194,10 @@ fn guess_worker(
let guess_result = pool.install(|| {
rayon::iter::repeat(0)
.map_init(
|| {
(
block_body_mast_hash_digest,
appendix_digest,
&block_header_template,
rand::thread_rng(),
)
},
|(block_body_mast_hash_digest_, appendix_digest_, block_header_template_, rng),
_x| {
|| (&block_header_template, rand::thread_rng()),
|(block_header_template_, rng), _i| {
guess_nonce_iteration(
*block_body_mast_hash_digest_,
*appendix_digest_,
kernel_auth_path,
block_header_template_.clone(),
&previous_block_header,
&sender,
Expand All @@ -199,6 +207,7 @@ fn guess_worker(
},
sleepy_guessing,
rng,
header_auth_path,
)
},
)
Expand Down Expand Up @@ -285,6 +294,25 @@ impl GuessNonceResult {
}
}

#[inline(always)]
fn fast_mast_hash(
kernel_auth_path: [Digest; 2],
header_auth_path: [Digest; 3],
nonce: Digest,
) -> Digest {
let header_mast_hash = Tip5::hash_pair(Tip5::hash_varlen(&nonce.encode()), header_auth_path[0]);
let header_mast_hash = Tip5::hash_pair(header_mast_hash, header_auth_path[1]);
let header_mast_hash = Tip5::hash_pair(header_auth_path[2], header_mast_hash);

Tip5::hash_pair(
Tip5::hash_pair(
Tip5::hash_varlen(&header_mast_hash.encode()),
kernel_auth_path[0],
),
kernel_auth_path[1],
)
}

/// Run a single iteration of the mining loop.
///
/// Returns (found: bool, cancelled: bool).
Expand All @@ -294,56 +322,54 @@ impl GuessNonceResult {
#[inline]
#[allow(clippy::too_many_arguments)]
fn guess_nonce_iteration(
block_body_mast_hash_digest: Digest,
appendix_digest: Digest,
kernel_auth_path: [Digest; 2],
mut block_header_template: BlockHeader,
previous_block_header: &BlockHeader,
sender: &oneshot::Sender<NewBlockFound>,
difficulty_info: DifficultyInfo,
sleepy_guessing: bool,
rng: &mut rand::rngs::ThreadRng,
mut bh_auth_path: [Digest; 3],
) -> GuessNonceResult {
if sender.is_canceled() {
info!(
"Abandoning mining of current block with height {}",
block_header_template.height
);
return GuessNonceResult::Cancelled;
}

// Modify the nonce in the block header. In order to collect the guesser
// fee, this nonce must be the post-image of a known pre-image under Tip5.
let nonce_preimage: Digest = rng.gen();
block_header_template.nonce = nonce_preimage.hash();

// See issue #149 and test block_timestamp_represents_time_block_found()
// this ensures header timestamp represents the moment block is found.
// this is simplest impl. Efficiencies can perhaps be gained by only
// performing every N iterations, or other strategies.
let now = Timestamp::now();
let new_difficulty = difficulty_control(
now,
previous_block_header.timestamp,
previous_block_header.difficulty,
difficulty_info.target_block_interval,
previous_block_header.height,
);
block_header_template.timestamp = now;
block_header_template.difficulty = new_difficulty;
let nonce = nonce_preimage.hash();

let digests = [
Tip5::hash_varlen(&block_header_template.mast_hash().encode()),
block_body_mast_hash_digest,
appendix_digest,
Digest::default(),
];
let block_hash = MerkleTree::par_new(&digests).unwrap().root();
let success = block_hash <= difficulty_info.threshold;
// Update some parameters on average every `N` guess.
if nonce.values()[0].raw_u64() % (1 << 20) == 0 {
// See issue #149 and test block_timestamp_represents_time_block_found()
// this ensures header timestamp represents the moment block is found.
// this is simplest impl.
let now = Timestamp::now();
let new_difficulty = difficulty_control(
now,
previous_block_header.timestamp,
previous_block_header.difficulty,
difficulty_info.target_block_interval,
previous_block_header.height,
);
block_header_template.timestamp = now;
block_header_template.difficulty = new_difficulty;

if sender.is_canceled() {
info!(
"Abandoning mining of current block with height {}",
block_header_template.height
);
return GuessNonceResult::Cancelled;
}

bh_auth_path = precalculate_header_ap(&block_header_template);
}

if sleepy_guessing {
std::thread::sleep(Duration::from_millis(100));
}

let block_hash = fast_mast_hash(kernel_auth_path, bh_auth_path, nonce);
let success = block_hash <= difficulty_info.threshold;

match success {
false => GuessNonceResult::BlockNotFound,
true => GuessNonceResult::BlockFound {
Expand Down Expand Up @@ -1022,11 +1048,12 @@ pub(crate) mod mine_loop_tests {

let (worker_task_tx, _worker_task_rx) = oneshot::channel::<NewBlockFound>();

let num_iterations_launched = 100_000;
let num_iterations_launched = 1_000_000;
let tick = std::time::SystemTime::now();
let previous_block_header = previous_block.header();
let block_header_template = block.header().to_owned();
let (block_body_mast_hash_digest, appendix_digest) = precalculate_mast_leafs(&block);
let (kernel_auth_path, header_auth_path) = precalculate_block_auth_paths(&block);

let num_iterations_run =
rayon::iter::IntoParallelIterator::into_par_iter(0..num_iterations_launched)
.map_init(
Expand All @@ -1037,10 +1064,9 @@ pub(crate) mod mine_loop_tests {
rand::thread_rng(),
)
},
|(prev_header, block_header_templ, prng), _| {
|(prev_header, block_header_templ, prng), _i| {
guess_nonce_iteration(
block_body_mast_hash_digest,
appendix_digest,
kernel_auth_path,
block_header_templ.to_owned(),
prev_header,
&worker_task_tx,
Expand All @@ -1050,6 +1076,7 @@ pub(crate) mod mine_loop_tests {
},
sleepy_guessing,
prng,
header_auth_path,
);
},
)
Expand Down

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