A HyperSharedPointer behaves like std::shared_ptr, but when the pointer is
shared many times across lots of threads, it is faster by as much as 9x.
Beware! Since HyperSharedPointer is slow to create and consumes a large
amount of memory, it is not a drop-in replacement for std::shared_ptr. Also,
support for a std::weak_ptr corollary is not yet complete.
The basic concept behind HyperSharedPointer is to shard the control-block
counter for a shared pointer across each CPU. When the pointer is heavily shared,
nearly all of the atomic counter operations will be uncontested.
$ bazel run -c opt :hyper_shared_pointer_benchmark -- --benchmark_min_time=1
2022-11-25T23:07:30-08:00
Running bazel-bin/hyper_shared_pointer_benchmark
Run on (12 X 4500 MHz CPU s)
CPU Caches:
L1 Data 32 KiB (x6)
L1 Instruction 32 KiB (x6)
L2 Unified 256 KiB (x6)
L3 Unified 12288 KiB (x1)
Load Average: 0.69, 0.70, 0.64
***WARNING*** CPU scaling is enabled, the benchmark real time measurements may be noisy and will incur extra overhead.
----------------------------------------------------------------------------------
Benchmark Time CPU Iterations
----------------------------------------------------------------------------------
BM_CreateStdSharedPtr/threads:1 24.9 ns 24.9 ns 56765746
BM_CreateStdSharedPtr/threads:12 5.19 ns 62.2 ns 24550152
BM_CreateHyperSharedPointer/threads:1 4509 ns 4506 ns 306655
BM_CreateHyperSharedPointer/threads:12 854 ns 9962 ns 149592
BM_SharingStdSharedPtr/threads:1 15.6 ns 15.6 ns 87822375
BM_SharingStdSharedPtr/threads:12 38.0 ns 456 ns 3195936
BM_SharingHyperSharedPointer/threads:1 26.9 ns 26.9 ns 51484835
BM_SharingHyperSharedPointer/threads:12 4.07 ns 48.9 ns 29400012
The BM_SharingStdSharedPtr/threads:12 and
BM_SharingHyperSharedPointer/threads:12 benchmarks model the hyper sharing use
case.