Merge #21170: bench: Add benchmark to write JSON into a string

e3e0a2432c587ee06e469c37ffae133b7ac55c77 Add benchmark to write JSON into a string (Martin Ankerl)

Pull request description:

  The benchmark `BlockToJsonVerbose` only tests generating (and destroying)
  the JSON data structure, but serializing into a string is also a
  performance critical aspect of the RPC calls.

  Extracts test setup into a `struct TestBlockAndIndex`, and uses it in
  both `BlockToJsonVerbose` and `BlockToJsonVerboseWrite`.

  Also, use `ankerl::nanobench::doNotOptimizeAway` to make sure the compiler
  can't optimize the result of the calls away.

  Here are benchmark results on my Intel i7-8700:

  |               ns/op |                op/s |    err% |          ins/op |          cyc/op |    IPC |         bra/op |   miss% |     total | benchmark
  |--------------------:|--------------------:|--------:|----------------:|----------------:|-------:|---------------:|--------:|----------:|:----------
  |       71,807,017.00 |               13.93 |    0.4% |  555,782,961.00 |  220,788,645.00 |  2.517 | 102,279,341.00 |    0.4% |      0.80 | `BlockToJsonVerbose`
  |       27,916,835.00 |               35.82 |    0.1% |  235,084,034.00 |   89,033,525.00 |  2.640 |  42,911,139.00 |    0.3% |      0.32 | `BlockToJsonVerboseWrite`

ACKs for top commit:
  laanwj:
    Code review ACK e3e0a2432c587ee06e469c37ffae133b7ac55c77

Tree-SHA512: bc4d6d1588d47d4bd7af8e7908e44b8561bc391a2d73eccd7c0aa37fc40e8a9ce1fa1f3c29b416eef24a73c6bce3036839c0bbfe1b8dbd6d1bba3718b7ca5383

src/bench/rpc_blockchain.cpp

@@ -12,25 +12,49 @@
 
 #include <univalue.h>
 
+namespace {
+
+struct TestBlockAndIndex {
+    TestingSetup test_setup{};
+    CBlock block{};
+    uint256 blockHash{};
+    CBlockIndex blockindex{};
+
+    TestBlockAndIndex()
+    {
+        CDataStream stream(benchmark::data::block413567, SER_NETWORK, PROTOCOL_VERSION);
+        char a = '\0';
+        stream.write(&a, 1); // Prevent compaction
+
+        stream >> block;
+
+        blockHash = block.GetHash();
+        blockindex.phashBlock = &blockHash;
+        blockindex.nBits = 403014710;
+    }
+};
+
+} // namespace
+
 static void BlockToJsonVerbose(benchmark::Bench& bench)
 {
-    TestingSetup test_setup{};
+    TestBlockAndIndex data;
-
-    CDataStream stream(benchmark::data::block413567, SER_NETWORK, PROTOCOL_VERSION);
-    char a = '\0';
-    stream.write(&a, 1); // Prevent compaction
-
-    CBlock block;
-    stream >> block;
-
-    CBlockIndex blockindex;
-    const uint256 blockHash = block.GetHash();
-    blockindex.phashBlock = &blockHash;
-    blockindex.nBits = 403014710;
-
     bench.run([&] {
-        (void)blockToJSON(block, &blockindex, &blockindex, /*verbose*/ true);
+        auto univalue = blockToJSON(data.block, &data.blockindex, &data.blockindex, /*verbose*/ true);
+        ankerl::nanobench::doNotOptimizeAway(univalue);
     });
 }
 
 BENCHMARK(BlockToJsonVerbose);
+
+static void BlockToJsonVerboseWrite(benchmark::Bench& bench)
+{
+    TestBlockAndIndex data;
+    auto univalue = blockToJSON(data.block, &data.blockindex, &data.blockindex, /*verbose*/ true);
+    bench.run([&] {
+        auto str = univalue.write();
+        ankerl::nanobench::doNotOptimizeAway(str);
+    });
+}
+
+BENCHMARK(BlockToJsonVerboseWrite);