[PATCH] D140271: [NFCI][llvm-exegesis] Benchmark: parallelize codegen (5x ... 8x less wallclock)

[Roman Lebedev via Phabricator via llvm-commits]

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(i'd be fine just committing this, but just in case, for greater visibility if nothing else, decided to post)

We *might* not want to perform codegen for all Configurations X Repetitions
beforehand, since the produced Runnable Configurations may have significant
file sizes (up to 1MB?), and there are many Runnable Configurations (30k?).
But doing batches is fine memory-wise, and is a win, as expected.

We really don't want to smudge the measurements, so we do those
standalone, without running *anything* else in parallel,
but when not measuring, the codegen can be done in parallel.

Special care is taken to not produce snippets in non-deterministic order,
although snippets themselves are randomized, it's not as useful.

And so it becomes almost real-time:

`time ./bin/llvm-exegesis --opcode-index=-1 --mode=latency --repetition-mode=duplicate  --dump-object-to-disk=0 --benchmarks-file=/tmp/res-new.yaml --measurements-print-progress  --max-configs-per-opcode=8192`

old:

  real    1m33.500s
  user    1m29.644s
  sys     0m1.762s

new:

  real    0m18.191s
  user    3m8.253s
  sys     0m3.999s

(5.1x)

`time ./bin/llvm-exegesis --opcode-index=-1 --mode=uops --repetition-mode=duplicate  --dump-object-to-disk=0 --benchmarks-file=/tmp/res-new.yaml --measurements-print-progress`

old:

  real    1m52.256s
  user    1m48.518s
  sys     0m1.479s

new:

  real    0m13.273s
  user    4m14.228s
  sys     0m4.903s

(8.5x)

`time ./bin/llvm-exegesis --opcode-index=-1 --mode=inverse_throughput --repetition-mode=duplicate  --dump-object-to-disk=0 --benchmarks-file=/tmp/res-new.yaml --measurements-print-progress`

old:

  real    1m58.765s
  user    1m53.259s
  sys     0m2.937s

new:

  real    0m19.586s
  user    4m19.133s
  sys     0m6.314s

(6x)


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D140271

Files:
  llvm/tools/llvm-exegesis/llvm-exegesis.cpp

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