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-rw-r--r--absl/hash/BUILD.bazel18
-rw-r--r--absl/hash/hash_benchmark.cc249
2 files changed, 267 insertions, 0 deletions
diff --git a/absl/hash/BUILD.bazel b/absl/hash/BUILD.bazel
index 40c8f207..acd490ba 100644
--- a/absl/hash/BUILD.bazel
+++ b/absl/hash/BUILD.bazel
@@ -82,6 +82,24 @@ cc_test(
],
)
+cc_binary(
+ name = "hash_benchmark",
+ testonly = 1,
+ srcs = ["hash_benchmark.cc"],
+ copts = ABSL_TEST_COPTS,
+ linkopts = ABSL_DEFAULT_LINKOPTS,
+ tags = ["benchmark"],
+ visibility = ["//visibility:private"],
+ deps = [
+ ":hash",
+ "//absl/base:core_headers",
+ "//absl/random",
+ "//absl/strings:cord",
+ "//absl/strings:cord_test_helpers",
+ "@com_github_google_benchmark//:benchmark_main",
+ ],
+)
+
cc_library(
name = "spy_hash_state",
testonly = 1,
diff --git a/absl/hash/hash_benchmark.cc b/absl/hash/hash_benchmark.cc
new file mode 100644
index 00000000..27e52719
--- /dev/null
+++ b/absl/hash/hash_benchmark.cc
@@ -0,0 +1,249 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <typeindex>
+
+#include "absl/base/attributes.h"
+#include "absl/hash/hash.h"
+#include "absl/random/random.h"
+#include "absl/strings/cord.h"
+#include "absl/strings/cord_test_helpers.h"
+#include "benchmark/benchmark.h"
+
+namespace {
+
+using absl::Hash;
+
+template <template <typename> class H, typename T>
+void RunBenchmark(benchmark::State& state, T value) {
+ H<T> h;
+ for (auto _ : state) {
+ benchmark::DoNotOptimize(value);
+ benchmark::DoNotOptimize(h(value));
+ }
+}
+
+} // namespace
+
+template <typename T>
+using AbslHash = absl::Hash<T>;
+
+class TypeErasedInterface {
+ public:
+ virtual ~TypeErasedInterface() = default;
+
+ template <typename H>
+ friend H AbslHashValue(H state, const TypeErasedInterface& wrapper) {
+ state = H::combine(std::move(state), std::type_index(typeid(wrapper)));
+ wrapper.HashValue(absl::HashState::Create(&state));
+ return state;
+ }
+
+ private:
+ virtual void HashValue(absl::HashState state) const = 0;
+};
+
+template <typename T>
+struct TypeErasedAbslHash {
+ class Wrapper : public TypeErasedInterface {
+ public:
+ explicit Wrapper(const T& value) : value_(value) {}
+
+ private:
+ void HashValue(absl::HashState state) const override {
+ absl::HashState::combine(std::move(state), value_);
+ }
+
+ const T& value_;
+ };
+
+ size_t operator()(const T& value) {
+ return absl::Hash<Wrapper>{}(Wrapper(value));
+ }
+};
+
+template <typename FuncType>
+inline FuncType* ODRUseFunction(FuncType* ptr) {
+ volatile FuncType* dummy = ptr;
+ return dummy;
+}
+
+absl::Cord FlatCord(size_t size) {
+ absl::Cord result(std::string(size, 'a'));
+ result.Flatten();
+ return result;
+}
+
+absl::Cord FragmentedCord(size_t size) {
+ const size_t orig_size = size;
+ std::vector<std::string> chunks;
+ size_t chunk_size = std::max<size_t>(1, size / 10);
+ while (size > chunk_size) {
+ chunks.push_back(std::string(chunk_size, 'a'));
+ size -= chunk_size;
+ }
+ if (size > 0) {
+ chunks.push_back(std::string(size, 'a'));
+ }
+ absl::Cord result = absl::MakeFragmentedCord(chunks);
+ (void) orig_size;
+ assert(result.size() == orig_size);
+ return result;
+}
+
+// Generates a benchmark and a codegen method for the provided types. The
+// codegen method provides a well known entrypoint for dumping assembly.
+#define MAKE_BENCHMARK(hash, name, ...) \
+ namespace { \
+ void BM_##hash##_##name(benchmark::State& state) { \
+ RunBenchmark<hash>(state, __VA_ARGS__); \
+ } \
+ BENCHMARK(BM_##hash##_##name); \
+ } \
+ size_t Codegen##hash##name(const decltype(__VA_ARGS__)& arg); \
+ size_t Codegen##hash##name(const decltype(__VA_ARGS__)& arg) { \
+ return hash<decltype(__VA_ARGS__)>{}(arg); \
+ } \
+ bool absl_hash_test_odr_use##hash##name = \
+ ODRUseFunction(&Codegen##hash##name);
+
+MAKE_BENCHMARK(AbslHash, Int32, int32_t{});
+MAKE_BENCHMARK(AbslHash, Int64, int64_t{});
+MAKE_BENCHMARK(AbslHash, Double, 1.2);
+MAKE_BENCHMARK(AbslHash, DoubleZero, 0.0);
+MAKE_BENCHMARK(AbslHash, PairInt32Int32, std::pair<int32_t, int32_t>{});
+MAKE_BENCHMARK(AbslHash, PairInt64Int64, std::pair<int64_t, int64_t>{});
+MAKE_BENCHMARK(AbslHash, TupleInt32BoolInt64,
+ std::tuple<int32_t, bool, int64_t>{});
+MAKE_BENCHMARK(AbslHash, String_0, std::string());
+MAKE_BENCHMARK(AbslHash, String_10, std::string(10, 'a'));
+MAKE_BENCHMARK(AbslHash, String_30, std::string(30, 'a'));
+MAKE_BENCHMARK(AbslHash, String_90, std::string(90, 'a'));
+MAKE_BENCHMARK(AbslHash, String_200, std::string(200, 'a'));
+MAKE_BENCHMARK(AbslHash, String_5000, std::string(5000, 'a'));
+MAKE_BENCHMARK(AbslHash, Cord_Flat_0, absl::Cord());
+MAKE_BENCHMARK(AbslHash, Cord_Flat_10, FlatCord(10));
+MAKE_BENCHMARK(AbslHash, Cord_Flat_30, FlatCord(30));
+MAKE_BENCHMARK(AbslHash, Cord_Flat_90, FlatCord(90));
+MAKE_BENCHMARK(AbslHash, Cord_Flat_200, FlatCord(200));
+MAKE_BENCHMARK(AbslHash, Cord_Flat_5000, FlatCord(5000));
+MAKE_BENCHMARK(AbslHash, Cord_Fragmented_200, FragmentedCord(200));
+MAKE_BENCHMARK(AbslHash, Cord_Fragmented_5000, FragmentedCord(5000));
+MAKE_BENCHMARK(AbslHash, VectorInt64_10, std::vector<int64_t>(10));
+MAKE_BENCHMARK(AbslHash, VectorInt64_100, std::vector<int64_t>(100));
+MAKE_BENCHMARK(AbslHash, VectorDouble_10, std::vector<double>(10, 1.1));
+MAKE_BENCHMARK(AbslHash, VectorDouble_100, std::vector<double>(100, 1.1));
+MAKE_BENCHMARK(AbslHash, PairStringString_0,
+ std::make_pair(std::string(), std::string()));
+MAKE_BENCHMARK(AbslHash, PairStringString_10,
+ std::make_pair(std::string(10, 'a'), std::string(10, 'b')));
+MAKE_BENCHMARK(AbslHash, PairStringString_30,
+ std::make_pair(std::string(30, 'a'), std::string(30, 'b')));
+MAKE_BENCHMARK(AbslHash, PairStringString_90,
+ std::make_pair(std::string(90, 'a'), std::string(90, 'b')));
+MAKE_BENCHMARK(AbslHash, PairStringString_200,
+ std::make_pair(std::string(200, 'a'), std::string(200, 'b')));
+MAKE_BENCHMARK(AbslHash, PairStringString_5000,
+ std::make_pair(std::string(5000, 'a'), std::string(5000, 'b')));
+
+MAKE_BENCHMARK(TypeErasedAbslHash, Int32, int32_t{});
+MAKE_BENCHMARK(TypeErasedAbslHash, Int64, int64_t{});
+MAKE_BENCHMARK(TypeErasedAbslHash, PairInt32Int32,
+ std::pair<int32_t, int32_t>{});
+MAKE_BENCHMARK(TypeErasedAbslHash, PairInt64Int64,
+ std::pair<int64_t, int64_t>{});
+MAKE_BENCHMARK(TypeErasedAbslHash, TupleInt32BoolInt64,
+ std::tuple<int32_t, bool, int64_t>{});
+MAKE_BENCHMARK(TypeErasedAbslHash, String_0, std::string());
+MAKE_BENCHMARK(TypeErasedAbslHash, String_10, std::string(10, 'a'));
+MAKE_BENCHMARK(TypeErasedAbslHash, String_30, std::string(30, 'a'));
+MAKE_BENCHMARK(TypeErasedAbslHash, String_90, std::string(90, 'a'));
+MAKE_BENCHMARK(TypeErasedAbslHash, String_200, std::string(200, 'a'));
+MAKE_BENCHMARK(TypeErasedAbslHash, String_5000, std::string(5000, 'a'));
+MAKE_BENCHMARK(TypeErasedAbslHash, VectorDouble_10,
+ std::vector<double>(10, 1.1));
+MAKE_BENCHMARK(TypeErasedAbslHash, VectorDouble_100,
+ std::vector<double>(100, 1.1));
+
+// The latency benchmark attempts to model the speed of the hash function in
+// production. When a hash function is used for hashtable lookups it is rarely
+// used to hash N items in a tight loop nor on constant sized strings. Instead,
+// after hashing there is a potential equality test plus a (usually) large
+// amount of user code. To simulate this effectively we introduce a data
+// dependency between elements we hash by using the hash of the Nth element as
+// the selector of the N+1th element to hash. This isolates the hash function
+// code much like in production. As a bonus we use the hash to generate strings
+// of size [1,N] (instead of fixed N) to disable perfect branch predictions in
+// hash function implementations.
+namespace {
+// 16kb fits in L1 cache of most CPUs we care about. Keeping memory latency low
+// will allow us to attribute most time to CPU which means more accurate
+// measurements.
+static constexpr size_t kEntropySize = 16 << 10;
+static char entropy[kEntropySize + 1024];
+ABSL_ATTRIBUTE_UNUSED static const bool kInitialized = [] {
+ absl::BitGen gen;
+ static_assert(sizeof(entropy) % sizeof(uint64_t) == 0, "");
+ for (int i = 0; i != sizeof(entropy); i += sizeof(uint64_t)) {
+ auto rand = absl::Uniform<uint64_t>(gen);
+ memcpy(&entropy[i], &rand, sizeof(uint64_t));
+ }
+ return true;
+}();
+} // namespace
+
+template <class T>
+struct PodRand {
+ static_assert(std::is_pod<T>::value, "");
+ static_assert(kEntropySize + sizeof(T) < sizeof(entropy), "");
+
+ T Get(size_t i) const {
+ T v;
+ memcpy(&v, &entropy[i % kEntropySize], sizeof(T));
+ return v;
+ }
+};
+
+template <size_t N>
+struct StringRand {
+ static_assert(kEntropySize + N < sizeof(entropy), "");
+
+ absl::string_view Get(size_t i) const {
+ // This has a small bias towards small numbers. Because max N is ~200 this
+ // is very small and prefer to be very fast instead of absolutely accurate.
+ // Also we pass N = 2^K+1 so that mod reduces to a bitand.
+ size_t s = (i % (N - 1)) + 1;
+ return {&entropy[i % kEntropySize], s};
+ }
+};
+
+#define MAKE_LATENCY_BENCHMARK(hash, name, ...) \
+ namespace { \
+ void BM_latency_##hash##_##name(benchmark::State& state) { \
+ __VA_ARGS__ r; \
+ hash<decltype(r.Get(0))> h; \
+ size_t i = 871401241; \
+ for (auto _ : state) { \
+ benchmark::DoNotOptimize(i = h(r.Get(i))); \
+ } \
+ } \
+ BENCHMARK(BM_latency_##hash##_##name); \
+ } // namespace
+
+MAKE_LATENCY_BENCHMARK(AbslHash, Int32, PodRand<int32_t>);
+MAKE_LATENCY_BENCHMARK(AbslHash, Int64, PodRand<int64_t>);
+MAKE_LATENCY_BENCHMARK(AbslHash, String9, StringRand<9>);
+MAKE_LATENCY_BENCHMARK(AbslHash, String33, StringRand<33>);
+MAKE_LATENCY_BENCHMARK(AbslHash, String65, StringRand<65>);
+MAKE_LATENCY_BENCHMARK(AbslHash, String257, StringRand<257>);
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-28 01:18:31 +0000