Hakyll.Core.Runtime: use MVar instead of TVar

[vaibhavsagar]

Proposing a slightly different choice of concurrent variable type to #844.

[vaibhavsagar]

quick benchmarks on my own site at https://github.com/vaibhavsagar/website, result-new is this PR and result-old is d739fd1:

[nix-shell:~/code/website]$ hyperfine --prepare './result-new/bin/site clean' './result-new/bin/site build' --prepare './result-old/bin/site clean' './result-old/bin/site build'
Benchmark #1: ./result-new/bin/site build
  Time (mean ± σ):      3.335 s ±  0.306 s    [User: 17.169 s, System: 4.343 s]
  Range (min … max):    3.036 s …  4.075 s    10 runs
 
Benchmark #2: ./result-old/bin/site build
  Time (mean ± σ):      3.434 s ±  0.213 s    [User: 17.648 s, System: 4.595 s]
  Range (min … max):    3.106 s …  3.734 s    10 runs
 
Summary
  './result-new/bin/site build' ran
    1.03 ± 0.11 times faster than './result-old/bin/site build'

[vaibhavsagar]

Huh, I tried running it again in the other order and it gave me the opposite result:

[nix-shell:~/code/website]$ hyperfine --prepare './result-old/bin/site clean' './result-old/bin/site build' --prepare './result-new/bin/site clean' './result-new/bin/site build'
Benchmark #1: ./result-old/bin/site build
  Time (mean ± σ):      3.447 s ±  0.288 s    [User: 17.842 s, System: 4.563 s]
  Range (min … max):    3.117 s …  4.135 s    10 runs
 
Benchmark #2: ./result-new/bin/site build
  Time (mean ± σ):      3.515 s ±  0.289 s    [User: 18.079 s, System: 4.467 s]
  Range (min … max):    3.096 s …  4.027 s    10 runs
 
Summary
  './result-old/bin/site build' ran
    1.02 ± 0.12 times faster than './result-new/bin/site build'

[Minoru]

I still don't know anything about async Haskell, but I read the Control.Concurrent.MVar doc and these changes look okay. So I'll merge this.

Huh, I tried running it again in the other order and it gave me the opposite result:

Your environment is probably noisy. On my machine, MVar consistently out-performs TVar by 3–4%:

$ hyperfine --prepare './debiania-old clean' './debiania-old build +RTS -N4' --prepare './debiania-new clean' './debiania-new build +RTS -N4'
Benchmark #1: ./debiania-old build +RTS -N4
  Time (mean ± σ):     10.344 s ±  0.246 s    [User: 21.688 s, System: 4.336 s]
  Range (min … max):    9.992 s … 10.654 s    10 runs

Benchmark #2: ./debiania-new build +RTS -N4
  Time (mean ± σ):     10.077 s ±  0.329 s    [User: 21.009 s, System: 4.331 s]
  Range (min … max):    9.502 s … 10.674 s    10 runs

Summary
  './debiania-new build +RTS -N4' ran
    1.03 ± 0.04 times faster than './debiania-old build +RTS -N4'
$ hyperfine --prepare './debiania-new clean' './debiania-new build +RTS -N4' --prepare './debiania-old clean' './debiania-old build +RTS -N4'
Benchmark #1: ./debiania-new build +RTS -N4
  Time (mean ± σ):      9.973 s ±  0.312 s    [User: 20.773 s, System: 4.183 s]
  Range (min … max):    9.432 s … 10.505 s    10 runs

Benchmark #2: ./debiania-old build +RTS -N4
  Time (mean ± σ):     10.332 s ±  0.293 s    [User: 21.484 s, System: 4.463 s]
  Range (min … max):    9.759 s … 10.690 s    10 runs

Summary
  './debiania-new build +RTS -N4' ran
    1.04 ± 0.04 times faster than './debiania-old build +RTS -N4'

I was hoping that MVar might fix #850, but no:

$ hyperfine --parameter-scan threads 1 10 --prepare './debiania-new clean' './debiania-new build +RTS -N{threads}'
Benchmark #1: ./debiania-new build +RTS -N1
  Time (mean ± σ):     14.021 s ±  0.334 s    [User: 13.887 s, System: 0.646 s]
  Range (min … max):   13.369 s … 14.643 s    10 runs

Benchmark #2: ./debiania-new build +RTS -N2
  Time (mean ± σ):     10.909 s ±  0.208 s    [User: 15.330 s, System: 1.907 s]
  Range (min … max):   10.632 s … 11.317 s    10 runs

Benchmark #3: ./debiania-new build +RTS -N3
  Time (mean ± σ):     10.120 s ±  0.251 s    [User: 17.742 s, System: 2.916 s]
  Range (min … max):    9.804 s … 10.511 s    10 runs

Benchmark #4: ./debiania-new build +RTS -N4
  Time (mean ± σ):     10.118 s ±  0.281 s    [User: 21.168 s, System: 4.287 s]
  Range (min … max):    9.481 s … 10.495 s    10 runs

Benchmark #5: ./debiania-new build +RTS -N5
  Time (mean ± σ):     10.636 s ±  0.220 s    [User: 26.352 s, System: 6.382 s]
  Range (min … max):   10.223 s … 10.922 s    10 runs

Benchmark #6: ./debiania-new build +RTS -N6
  Time (mean ± σ):     10.910 s ±  0.298 s    [User: 30.955 s, System: 8.487 s]
  Range (min … max):   10.533 s … 11.466 s    10 runs

Benchmark #7: ./debiania-new build +RTS -N7
  Time (mean ± σ):     11.228 s ±  0.193 s    [User: 36.000 s, System: 10.565 s]
  Range (min … max):   10.925 s … 11.554 s    10 runs

Benchmark #8: ./debiania-new build +RTS -N8
  Time (mean ± σ):     12.273 s ±  0.264 s    [User: 46.391 s, System: 12.316 s]
  Range (min … max):   11.845 s … 12.555 s    10 runs

Benchmark #9: ./debiania-new build +RTS -N9
  Time (mean ± σ):     13.482 s ±  0.183 s    [User: 52.771 s, System: 14.147 s]
  Range (min … max):   13.183 s … 13.845 s    10 runs

Benchmark #10: ./debiania-new build +RTS -N10
  Time (mean ± σ):     14.051 s ±  0.113 s    [User: 56.190 s, System: 14.633 s]
  Range (min … max):   13.815 s … 14.212 s    10 runs

Summary
  './debiania-new build +RTS -N4' ran
    1.00 ± 0.04 times faster than './debiania-new build +RTS -N3'
    1.05 ± 0.04 times faster than './debiania-new build +RTS -N5'
    1.08 ± 0.04 times faster than './debiania-new build +RTS -N2'
    1.08 ± 0.04 times faster than './debiania-new build +RTS -N6'
    1.11 ± 0.04 times faster than './debiania-new build +RTS -N7'
    1.21 ± 0.04 times faster than './debiania-new build +RTS -N8'
    1.33 ± 0.04 times faster than './debiania-new build +RTS -N9'
    1.39 ± 0.05 times faster than './debiania-new build +RTS -N1'
    1.39 ± 0.04 times faster than './debiania-new build +RTS -N10'

[Minoru]

Thank you @vaibhavsagar!

[vaibhavsagar]

My pleasure!