[libcxx-commits] [PATCH] D89110: [libcxx][dsl] Reduce number of feature checks

[Alexander Richardson via Phabricator via libcxx-commits]

arichardson added a comment.

In D89110#2322098 <https://reviews.llvm.org/D89110#2322098>, @ldionne wrote:

> What's the time gain like for doing this?

Measuring with perf on a Linux machine I get the following without (rG0db08e59c9d2d3b004ea61f96d823edff283ed25 <https://reviews.llvm.org/rG0db08e59c9d2d3b004ea61f96d823edff283ed25>):

  Performance counter stats for './bin/llvm-lit -v --no-execute projects/libcxx/test/libcxx/selftest/dsl/' (10 runs):
  
        3001.646813      task-clock (msec)         #    0.971 CPUs utilized            ( +-  0.68% )
                530      context-switches          #    0.177 K/sec                    ( +-  0.20% )
                 37      cpu-migrations            #    0.012 K/sec                    ( +-  8.62% )
            223,059      page-faults               #    0.074 M/sec                    ( +-  0.01% )
      5,421,406,209      cycles                    #    1.806 GHz                      ( +-  0.26% )
      5,856,892,943      instructions              #    1.08  insn per cycle           ( +-  0.01% )
      1,168,779,209      branches                  #  389.379 M/sec                    ( +-  0.01% )
         30,692,873      branch-misses             #    2.63% of all branches          ( +-  0.02% )
  
        3.091204859 seconds time elapsed                                          ( +-  0.72% )

And the following with the patch:

  Performance counter stats for './bin/llvm-lit -v --no-execute projects/libcxx/test/libcxx/selftest/dsl/' (10 runs):
  
        2833.725264      task-clock (msec)         #    0.968 CPUs utilized            ( +-  0.62% )
                503      context-switches          #    0.178 K/sec                    ( +-  0.42% )
                 29      cpu-migrations            #    0.010 K/sec                    ( +- 12.05% )
            208,416      page-faults               #    0.074 M/sec                    ( +-  0.01% )
      5,135,758,720      cycles                    #    1.812 GHz                      ( +-  0.20% )
      5,564,092,379      instructions              #    1.08  insn per cycle           ( +-  0.01% )
      1,112,432,802      branches                  #  392.569 M/sec                    ( +-  0.01% )
         29,604,154      branch-misses             #    2.66% of all branches          ( +-  0.04% )
  
        2.928603087 seconds time elapsed                                          ( +-  0.70% )

So almost 200ms here. The difference is probably bigger because the first measurements had my locale detection changes applied and this one didn't.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D89110/new/

https://reviews.llvm.org/D89110