[libcxx-commits] [libcxx] [libc++][pstl] Add more benchmarks of the parallel algorithms (PR #225908)

[Louis Dionne via libcxx-commits]

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@@ -0,0 +1,72 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: std-at-least-c++20
+
+// UNSUPPORTED: libcpp-has-no-incomplete-pstl
+
+#include <algorithm>
+#include <cstddef>
+#include <cstdint>
+#include <string>
+#include <vector>
+#include <execution>
+#include <utility>
+
+#include <benchmark/benchmark.h>
+
+#include "common.h"
+#include "test_macros.h"
+
+int main(int argc, char** argv) {
+  auto bm = [](std::string name, auto&& policy, auto generate_data) {
+    benchmark::RegisterBenchmark(
+        name,
+        [&policy, generate_data](auto& st) mutable {
+          std::size_t size      = st.range(0);
+          std::vector<int> data = generate_data(size);
+          std::vector<int> c    = data;
+
+          for ([[maybe_unused]] auto _ : st) {
+            benchmark::DoNotOptimize(c);
+            std::sort(policy, c.begin(), c.end());
+            benchmark::DoNotOptimize(c);
+
+            // Reset c to its original unsorted state
+            st.PauseTiming();
----------------
ldionne wrote:

`st.PauseTiming();` is really expensive -- we've been investigating serial benchmarks where we ended up only measuring the cost of `PauseTiming()` / `ResumeTiming()`.

At 64 elements, it's not clear to me that we're measuring anything meaningful as-is. I would recommend either using the batched approach we use in the serial benchmarks, or dropping the 64 size from here. If we drop 64, we should also add a comment explaining that we assume `PauseTiming` isn't dominating the benchmark.

https://github.com/llvm/llvm-project/pull/225908