Illuminating the processor core with LLVM-mca

(abseil.io)

65 points | by ckennelly 2 days ago ago

5 comments

  • KeplerBoy 2 days ago ago

    Also nicely demonstrated in godbolt's currently ongoing Advent of compiler optimizations series.

  • fweimer 2 days ago ago

    Wouldn't LLVM adjust the models if it is beneficial to its code generation, even if the result less accurately reflects the processor? (I think GCC does that.)

  • alain94040 2 days ago ago

    This is interesting if quite incomplete (as noted in the end conclusion). CPU re-order buffers turn what you think as mostly sequential execution into a massively parallel engine. Data memory access, perfecting, speculative execution, etc. But if you are running a micro-bencmark with a tight loop of millions of iterations, then understanding the pipeline dependencies and dispatching can provide good insights.

    • drob518 a day ago ago

      Yep. Cache is always the wildcard.

  • esbranson 2 days ago ago

    Too bad they don't support LC-3 or DLX. More my level lol. So begins another deep dive side quest with the chatbot into a tool I didn't even know existed.