elements/src/bench/cluster_linearize.cpp

// Copyright (c) The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#include <bench/bench.h>

#include <util/bitset.h>
#include <cluster_linearize.h>

using namespace cluster_linearize;

namespace {

/** Construct a linear graph. These are pessimal for AncestorCandidateFinder, as they maximize
 *  the number of ancestor set feerate updates. The best ancestor set is always the topmost
 *  remaining transaction, whose removal requires updating all remaining transactions' ancestor
 *  set feerates. */
template<typename SetType>
DepGraph<SetType> MakeLinearGraph(ClusterIndex ntx)
{
    DepGraph<SetType> depgraph;
    for (ClusterIndex i = 0; i < ntx; ++i) {
        depgraph.AddTransaction({-int32_t(i), 1});
        if (i > 0) depgraph.AddDependency(i - 1, i);
    }
    return depgraph;
}

// Construct a difficult graph. These need at least sqrt(2^(n-1)) iterations in the best
// known algorithms (purely empirically determined).
template<typename SetType>
DepGraph<SetType> MakeHardGraph(ClusterIndex ntx)
{
    DepGraph<SetType> depgraph;
    for (ClusterIndex i = 0; i < ntx; ++i) {
        if (ntx & 1) {
            // Odd cluster size.
            //
            // Mermaid diagram code for the resulting cluster for 11 transactions:
            // ```mermaid
            // graph BT
            // T0["T0: 1/2"];T1["T1: 14/2"];T2["T2: 6/1"];T3["T3: 5/1"];T4["T4: 7/1"];
            // T5["T5: 5/1"];T6["T6: 7/1"];T7["T7: 5/1"];T8["T8: 7/1"];T9["T9: 5/1"];
            // T10["T10: 7/1"];
            // T1-->T0;T1-->T2;T3-->T2;T4-->T3;T4-->T5;T6-->T5;T4-->T7;T8-->T7;T4-->T9;T10-->T9;
            // ```
            if (i == 0) {
                depgraph.AddTransaction({1, 2});
            } else if (i == 1) {
                depgraph.AddTransaction({14, 2});
                depgraph.AddDependency(0, 1);
            } else if (i == 2) {
                depgraph.AddTransaction({6, 1});
                depgraph.AddDependency(2, 1);
            } else if (i == 3) {
                depgraph.AddTransaction({5, 1});
                depgraph.AddDependency(2, 3);
            } else if ((i & 1) == 0) {
                depgraph.AddTransaction({7, 1});
                depgraph.AddDependency(i - 1, i);
            } else {
                depgraph.AddTransaction({5, 1});
                depgraph.AddDependency(i, 4);
            }
        } else {
            // Even cluster size.
            //
            // Mermaid diagram code for the resulting cluster for 10 transactions:
            // ```mermaid
            // graph BT
            // T0["T0: 1"];T1["T1: 3"];T2["T2: 1"];T3["T3: 4"];T4["T4: 0"];T5["T5: 4"];T6["T6: 0"];
            // T7["T7: 4"];T8["T8: 0"];T9["T9: 4"];
            // T1-->T0;T2-->T0;T3-->T2;T3-->T4;T5-->T4;T3-->T6;T7-->T6;T3-->T8;T9-->T8;
            // ```
            if (i == 0) {
                depgraph.AddTransaction({1, 1});
            } else if (i == 1) {
                depgraph.AddTransaction({3, 1});
                depgraph.AddDependency(0, 1);
            } else if (i == 2) {
                depgraph.AddTransaction({1, 1});
                depgraph.AddDependency(0, 2);
            } else if (i & 1) {
                depgraph.AddTransaction({4, 1});
                depgraph.AddDependency(i - 1, i);
            } else {
                depgraph.AddTransaction({0, 1});
                depgraph.AddDependency(i, 3);
            }
        }
    }
    return depgraph;
}

/** Benchmark that does search-based candidate finding with 10000 iterations.
 *
 * Its goal is measuring how much time every additional search iteration in linearization costs.
 */
template<typename SetType>
void BenchLinearizePerIterWorstCase(ClusterIndex ntx, benchmark::Bench& bench)
{
    const auto depgraph = MakeHardGraph<SetType>(ntx);
    const auto iter_limit = std::min<uint64_t>(10000, uint64_t{1} << (ntx / 2 - 1));
    bench.batch(iter_limit).unit("iters").run([&] {
        SearchCandidateFinder finder(depgraph);
        auto [candidate, iters_performed] = finder.FindCandidateSet(iter_limit, {});
        assert(iters_performed == iter_limit);
    });
}

/** Benchmark for linearization of a trivial linear graph using just ancestor sort.
 *
 * Its goal is measuring how much time linearization may take without any search iterations.
 *
 * If P is the resulting time of BenchLinearizePerIterWorstCase, and N is the resulting time of
 * BenchLinearizeNoItersWorstCase, then an invocation of Linearize with max_iterations=m should
 * take no more than roughly N+m*P time. This may however be an overestimate, as the worst cases
 * do not coincide (the ones that are worst for linearization without any search happen to be ones
 * that do not need many search iterations).
 */
template<typename SetType>
void BenchLinearizeNoItersWorstCase(ClusterIndex ntx, benchmark::Bench& bench)
{
    const auto depgraph = MakeLinearGraph<SetType>(ntx);
    bench.run([&] {
        Linearize(depgraph, /*max_iterations=*/0);
    });
}

} // namespace

static void LinearizePerIter16TxWorstCase(benchmark::Bench& bench) { BenchLinearizePerIterWorstCase<BitSet<16>>(16, bench); }
static void LinearizePerIter32TxWorstCase(benchmark::Bench& bench) { BenchLinearizePerIterWorstCase<BitSet<32>>(32, bench); }
static void LinearizePerIter48TxWorstCase(benchmark::Bench& bench) { BenchLinearizePerIterWorstCase<BitSet<48>>(48, bench); }
static void LinearizePerIter64TxWorstCase(benchmark::Bench& bench) { BenchLinearizePerIterWorstCase<BitSet<64>>(64, bench); }
static void LinearizePerIter75TxWorstCase(benchmark::Bench& bench) { BenchLinearizePerIterWorstCase<BitSet<75>>(75, bench); }
static void LinearizePerIter99TxWorstCase(benchmark::Bench& bench) { BenchLinearizePerIterWorstCase<BitSet<99>>(99, bench); }

static void LinearizeNoIters16TxWorstCase(benchmark::Bench& bench) { BenchLinearizeNoItersWorstCase<BitSet<16>>(16, bench); }
static void LinearizeNoIters32TxWorstCase(benchmark::Bench& bench) { BenchLinearizeNoItersWorstCase<BitSet<32>>(32, bench); }
static void LinearizeNoIters48TxWorstCase(benchmark::Bench& bench) { BenchLinearizeNoItersWorstCase<BitSet<48>>(48, bench); }
static void LinearizeNoIters64TxWorstCase(benchmark::Bench& bench) { BenchLinearizeNoItersWorstCase<BitSet<64>>(64, bench); }
static void LinearizeNoIters75TxWorstCase(benchmark::Bench& bench) { BenchLinearizeNoItersWorstCase<BitSet<75>>(75, bench); }
static void LinearizeNoIters99TxWorstCase(benchmark::Bench& bench) { BenchLinearizeNoItersWorstCase<BitSet<99>>(99, bench); }

BENCHMARK(LinearizePerIter16TxWorstCase, benchmark::PriorityLevel::HIGH);
BENCHMARK(LinearizePerIter32TxWorstCase, benchmark::PriorityLevel::HIGH);
BENCHMARK(LinearizePerIter48TxWorstCase, benchmark::PriorityLevel::HIGH);
BENCHMARK(LinearizePerIter64TxWorstCase, benchmark::PriorityLevel::HIGH);
BENCHMARK(LinearizePerIter75TxWorstCase, benchmark::PriorityLevel::HIGH);
BENCHMARK(LinearizePerIter99TxWorstCase, benchmark::PriorityLevel::HIGH);

BENCHMARK(LinearizeNoIters16TxWorstCase, benchmark::PriorityLevel::HIGH);
BENCHMARK(LinearizeNoIters32TxWorstCase, benchmark::PriorityLevel::HIGH);
BENCHMARK(LinearizeNoIters48TxWorstCase, benchmark::PriorityLevel::HIGH);
BENCHMARK(LinearizeNoIters64TxWorstCase, benchmark::PriorityLevel::HIGH);
BENCHMARK(LinearizeNoIters75TxWorstCase, benchmark::PriorityLevel::HIGH);
BENCHMARK(LinearizeNoIters99TxWorstCase, benchmark::PriorityLevel::HIGH);