2 ms·

Now comes big surprise: I just built it using LLVM under CLion IDE and the results are: G:\temp\cpp\rust-cpp-bench\cpp\cmake\cmake-build- release\fts_cma

by FpUser 4y ago

Now comes big surprise: I just built it using LLVM under CLion IDE and the results are: G:\temp\cpp\rust-cpp-bench\cpp\cmake\cmake-build- release\fts_cmake_cpp_bench.exe Totals: Overlaps: 220384338 By-Copy: 4397 By-Ref: 4396 Delta: -0.0227428% Process finished with exit code 0

josephg 4y ago
Why is performance so much better in this case? That seems like a suspiciously large delta from the first test. Were the other benchmarks run in debug mode / with optimizations turned off or something like that? What compiler & flags are you using?
- FpUser 4y ago
  >"Were the other benchmarks run in debug mode / with optimizations turned off or something like that?" Why would I do something like that? Of course all builds are release mode, optimize for speed. Rust - Windows - By-Copy: 14124, By-Borrow: 8150 C++ - Windows MS Compiler - By-Copy: 12160, By-Ref: 11423 C++ - Windows LLVM 15 - By-Copy: 4397, By-Ref: 4396 >"Why is performance so much better in this case?" Not sure and not in a mood to investigate. I do know if cache locality and branch prediction stars line up properly the performance difference can be staggering. Maybe LLVM has accomplished something nice in this department.
  - forrestthewoods 4y ago
    I just updated Visual Studio 2022 with all the latest updates and installed the Clang toolchain. I also updated Rust to latest. C++ MSVC: By-Copy: 12,077 By-Ref: 11,901 C++ Clang: By-Copy: 5,020 By-Ref: 5,029 Rust: By-Copy: 3,173 By-Borrow: 3,148 All on Windows, and on the same i7-8700k desktop I used for the original post in 2019. Your Rust numbers are particularly curious. Maybe run `rustup update` and try again?
    - FpUser 4y ago
      Just did this rustup update. Much better now. So the finals are: Rust - By-Copy: 2685, By-Borrow: 2694 C++ - Windows MS Compiler - By-Copy: 12160, By-Ref: 11423 C++ - Windows LLVM 15 - By-Copy: 4397, By-Ref: 4396 My CPU is AMD Ryzen 5950X so it seems like Rust kicks the shit out of C++ in this case. I am going to try LLVM 16 and GCC tomorrow. Happy New Year
      - forrestthewoods 4y ago
        Happy new year! If you dig deeper post here, or feel free to e-mail me. username @ gmail
        FpUser 4y ago
        No need to bother with LLVM16 and / or GCC. Enabling avx2 for Clang compiler produced following results that are more or less in line with what was expected. rust - By-Copy: 2683, By-Borrow: 2697 c++ - By-Copy: 2577, By-Ref: 2600 Either is way faster than the result from the original post and no rust does non win this "competition". C++ is a bit faster (see also the results from other poster above) but not by much.
      - dagome 4y ago
        Such stark difference in performance is really fishy and needs a deeper analysis. I just checked it with different compilers (all based on LLVM) and here are the results: rustc 1.58 (LLVM 13): By-Copy: 10804, By-Borrow: 7198 rustc 1.64 (LLVM 14): By-Copy: 7385, By-Borrow: 7328 rustc 1.66 (LLVM 15): By-Copy: 2667, By-Borrow: 2777 clang++ (LLVM 14): By-Copy: 2439, By-Ref: 2589 clang++ (LLVM 15): By-Copy: 2473, By-Ref: 2556 When compared with the same LLVM version clang much better utilised LLVM-14 than rustc - C++ is 3x faster. With LLVM-15 they are much closer.
        FpUser 4y ago
        Is this Windows or Linux? Also what CPU? Your results for rust on LLVM15 are pretty much close to mine but clang++ on LLVM15 is almost twice as slow. I really want to find reason.
  - kllrnohj 4y ago
    It may be the default fp mode for msvc is causing C++ to suffer here ( https://learn.microsoft.com/en-us/cpp/build/reference/fp-specify-floating-point-behavior?view=msvc-170 https://learn.microsoft.com/en-us/cpp/build/reference/fp-spe... ). It looks like the default behavior is quite conservative it what it allows to happen - like it won't even use FMAs with the default behavior?

by FpUser 4y ago

josephg 4y ago

Why is performance so much better in this case? That seems like a suspiciously large delta from the first test. Were the other benchmarks run in debug mode / with optimizations turned off or something like that? What compiler & flags are you using?

FpUser 4y ago
>"Were the other benchmarks run in debug mode / with optimizations turned off or something like that?" Why would I do something like that? Of course all builds are release mode, optimize for speed. Rust - Windows - By-Copy: 14124, By-Borrow: 8150 C++ - Windows MS Compiler - By-Copy: 12160, By-Ref: 11423 C++ - Windows LLVM 15 - By-Copy: 4397, By-Ref: 4396 >"Why is performance so much better in this case?" Not sure and not in a mood to investigate. I do know if cache locality and branch prediction stars line up properly the performance difference can be staggering. Maybe LLVM has accomplished something nice in this department.
- forrestthewoods 4y ago
  I just updated Visual Studio 2022 with all the latest updates and installed the Clang toolchain. I also updated Rust to latest. C++ MSVC: By-Copy: 12,077 By-Ref: 11,901 C++ Clang: By-Copy: 5,020 By-Ref: 5,029 Rust: By-Copy: 3,173 By-Borrow: 3,148 All on Windows, and on the same i7-8700k desktop I used for the original post in 2019. Your Rust numbers are particularly curious. Maybe run `rustup update` and try again?
  - FpUser 4y ago
    Just did this rustup update. Much better now. So the finals are: Rust - By-Copy: 2685, By-Borrow: 2694 C++ - Windows MS Compiler - By-Copy: 12160, By-Ref: 11423 C++ - Windows LLVM 15 - By-Copy: 4397, By-Ref: 4396 My CPU is AMD Ryzen 5950X so it seems like Rust kicks the shit out of C++ in this case. I am going to try LLVM 16 and GCC tomorrow. Happy New Year
    - forrestthewoods 4y ago
      Happy new year! If you dig deeper post here, or feel free to e-mail me. username @ gmail
      - FpUser 4y ago
        No need to bother with LLVM16 and / or GCC. Enabling avx2 for Clang compiler produced following results that are more or less in line with what was expected. rust - By-Copy: 2683, By-Borrow: 2697 c++ - By-Copy: 2577, By-Ref: 2600 Either is way faster than the result from the original post and no rust does non win this "competition". C++ is a bit faster (see also the results from other poster above) but not by much.
    - dagome 4y ago
      Such stark difference in performance is really fishy and needs a deeper analysis. I just checked it with different compilers (all based on LLVM) and here are the results: rustc 1.58 (LLVM 13): By-Copy: 10804, By-Borrow: 7198 rustc 1.64 (LLVM 14): By-Copy: 7385, By-Borrow: 7328 rustc 1.66 (LLVM 15): By-Copy: 2667, By-Borrow: 2777 clang++ (LLVM 14): By-Copy: 2439, By-Ref: 2589 clang++ (LLVM 15): By-Copy: 2473, By-Ref: 2556 When compared with the same LLVM version clang much better utilised LLVM-14 than rustc - C++ is 3x faster. With LLVM-15 they are much closer.
      - FpUser 4y ago
        Is this Windows or Linux? Also what CPU? Your results for rust on LLVM15 are pretty much close to mine but clang++ on LLVM15 is almost twice as slow. I really want to find reason.
- kllrnohj 4y ago
  It may be the default fp mode for msvc is causing C++ to suffer here ( https://learn.microsoft.com/en-us/cpp/build/reference/fp-specify-floating-point-behavior?view=msvc-170 https://learn.microsoft.com/en-us/cpp/build/reference/fp-spe... ). It looks like the default behavior is quite conservative it what it allows to happen - like it won't even use FMAs with the default behavior?