Async I/O queue

[tavianator]

See #101.

Performance

Performance is a work-in-progress; not every optimization from #101 is implemented yet. Here's a quick summary of the results so far:

• 9dca9f2 (eval: Pre-allocate the highest fd) saves hundreds of ms in some cases
• Complete traversal is already ~40% faster on large trees
• Early termination can be quite a bit faster (3-11x), though with higher variance
• Cold cache searches are also much faster (~40%)
• Depth-first search is quite a bit slower (3.8x)
  • Fixed: it helps to actually do any parallelism at all in depth-first mode ;)

Full benchmark results

Complete traversal

Small tree

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
bfs-main ~/code/bfs/history -false	4.2 ± 2.5	1.5	9.0	2.45 ± 2.38
bfs-ioq~2 ~/code/bfs/history -false	63.7 ± 11.6	36.7	95.2	37.44 ± 29.75
bfs-ioq~1 ~/code/bfs/history -false	5.0 ± 2.6	2.6	12.3	2.96 ± 2.74
bfs-ioq ~/code/bfs/history -false	1.7 ± 1.3	0.7	8.2	1.00

Medium tree

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
bfs-main ~/code/linux -false	65.9 ± 10.0	57.5	102.2	1.17 ± 0.27
bfs-ioq~2 ~/code/linux -false	248.3 ± 44.1	190.2	318.8	4.40 ± 1.10
bfs-ioq~1 ~/code/linux -false	86.1 ± 12.5	70.9	113.3	1.53 ± 0.35
bfs-ioq ~/code/linux -false	56.4 ± 9.9	44.3	74.9	1.00

Large tree

Command	Mean [s]	Min [s]	Max [s]	Relative
bfs-main ~/code/android -false	1.128 ± 0.032	1.091	1.192	1.42 ± 0.08
bfs-ioq~2 ~/code/android -false	1.563 ± 0.070	1.444	1.680	1.97 ± 0.12
bfs-ioq~1 ~/code/android -false	1.350 ± 0.055	1.283	1.433	1.70 ± 0.10
bfs-ioq ~/code/android -false	0.792 ± 0.035	0.739	0.851	1.00

Early termination

Shallow file

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
bfs-main ~/code/android -name ConstClassBenchmark.java -quit	129.6 ± 11.6	120.7	156.2	1.00
bfs-ioq~2 ~/code/android -name ConstClassBenchmark.java -quit	694.8 ± 586.9	179.3	1711.8	5.36 ± 4.55
bfs-ioq~1 ~/code/android -name ConstClassBenchmark.java -quit	364.9 ± 257.8	27.9	694.6	2.82 ± 2.01
bfs-ioq ~/code/android -name ConstClassBenchmark.java -quit	135.0 ± 162.7	14.8	802.8	1.04 ± 1.26

Medium file

Command	Mean [s]	Min [s]	Max [s]	Relative
bfs-main ~/code/android -name DominatorsComputation.java -quit	1.098 ± 0.023	1.073	1.141	11.41 ± 18.21
bfs-ioq~2 ~/code/android -name DominatorsComputation.java -quit	0.435 ± 0.324	0.259	1.276	4.52 ± 7.97
bfs-ioq~1 ~/code/android -name DominatorsComputation.java -quit	0.469 ± 0.482	0.080	1.067	4.87 ± 9.24
bfs-ioq ~/code/android -name DominatorsComputation.java -quit	0.096 ± 0.154	0.042	0.942	1.00

Deep file

Command	Mean [s]	Min [s]	Max [s]	Relative
bfs-main ~/code/android -name TestSidecarCompat.java -quit	1.351 ± 0.023	1.314	1.392	3.07 ± 1.98
bfs-ioq~2 ~/code/android -name TestSidecarCompat.java -quit	0.886 ± 0.562	0.262	1.587	2.01 ± 1.82
bfs-ioq~1 ~/code/android -name TestSidecarCompat.java -quit	0.501 ± 0.412	0.093	1.403	1.14 ± 1.19
bfs-ioq ~/code/android -name TestSidecarCompat.java -quit	0.441 ± 0.285	0.084	0.846	1.00

Search strategies

dfs

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
bfs-main -S dfs ~/code/linux -false	72.8 ± 13.5	60.3	101.8	1.34 ± 0.37
bfs-ioq~2 -S dfs ~/code/linux -false	100.7 ± 44.5	67.6	262.4	1.85 ± 0.90
bfs-ioq~1 -S dfs ~/code/linux -false	90.7 ± 11.6	70.5	112.0	1.67 ± 0.41
bfs-ioq -S dfs ~/code/linux -false	54.5 ± 11.4	37.0	75.5	1.00

ids

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
bfs-main -S ids ~/code/linux -false	358.5 ± 18.9	343.1	404.0	1.40 ± 0.08
bfs-ioq~2 -S ids ~/code/linux -false	612.4 ± 19.1	588.8	647.3	2.38 ± 0.09
bfs-ioq~1 -S ids ~/code/linux -false	440.1 ± 15.2	425.6	469.8	1.71 ± 0.07
bfs-ioq -S ids ~/code/linux -false	257.0 ± 6.0	247.5	264.4	1.00

eds

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
bfs-main -S eds ~/code/linux -false	139.8 ± 10.5	117.6	158.6	1.41 ± 0.22
bfs-ioq~2 -S eds ~/code/linux -false	319.5 ± 17.2	285.1	350.0	3.22 ± 0.47
bfs-ioq~1 -S eds ~/code/linux -false	159.0 ± 12.9	140.5	186.7	1.60 ± 0.25
bfs-ioq -S eds ~/code/linux -false	99.1 ± 13.3	79.3	135.5	1.00

Cold cache

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
bfs-main ~/code/linux -false	96.1 ± 9.3	86.0	110.8	1.39 ± 0.24
bfs-ioq~2 ~/code/linux -false	243.6 ± 40.2	197.2	337.4	3.51 ± 0.76
bfs-ioq~1 ~/code/linux -false	99.9 ± 11.9	85.4	121.6	1.44 ± 0.27
bfs-ioq ~/code/linux -false	69.4 ± 9.8	54.1	80.2	1.00