[all-commits] [llvm/llvm-project] 01d783: [llvm-profgen] Add --sample-period to estimate abs...

[Tim Creech via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 01d783643aa750aa160bdcd097176fcde934dbd1
      https://github.com/llvm/llvm-project/commit/01d783643aa750aa160bdcd097176fcde934dbd1
  Author: Tim Creech <timothy.m.creech at intel.com>
  Date:   2024-07-22 (Mon, 22 Jul 2024)

  Changed paths:
    A llvm/test/tools/llvm-profgen/period-scaling.test
    M llvm/tools/llvm-profgen/PerfReader.cpp

  Log Message:
  -----------
  [llvm-profgen] Add --sample-period to estimate absolute counts (#99826)

Without `--sample-period`, no assumptions are made about perf profile
sample frequencies. This is useful for comparing relative hotness of
different program locations within the same profile.

With `--sample-period`, LBR- and IP-based profile hit counts are
adjusted to estimate the absolute total event count for each program
location. This makes it reasonable to compare hit counts between
different profiles, e.g., between two LBR-based execution frequency
profiles with different sampling periods or between LBR-based execution
frequency profiles and IP-based branch mispredict profiles.

This functionality is in support of HWPGO[^1], which aims to enable
feedback from a wider range of hardware events.

[^1]:
https://llvm.org/devmtg/2024-04/slides/TechnicalTalks/Xiao-EnablingHW-BasedPGO.pdf



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