Performance!

[ghost]

Currently the work stealing scheduler has very odd scaling characteristics. I will place a * that these numbers are not realistic for a real application, since a real application would probably have more then a nop as a task. But still, the scheduler does not scale as well as I would have hoped.

1 thread

test bench_fibb_steal     ... bench:    291708 ns/iter (+/- 18080)
test chain_10_use_die     ... bench:     53808 ns/iter (+/- 5997)
test chain_10_wait        ... bench:     84236 ns/iter (+/- 5503)
test chain_1_000_use_die  ... bench:    421437 ns/iter (+/- 195312)
test chain_1_000_wait     ... bench:    418457 ns/iter (+/- 6165)
test fanout_1_000         ... bench:    596724 ns/iter (+/- 7209)
test repeat_100_x_100     ... bench:   7239210 ns/iter (+/- 5359287)
test repeat_1_000         ... bench:   1008281 ns/iter (+/- 330520)
test repeat_1_000_x_1_000 ... bench: 362229939 ns/iter (+/- 18925219)
test start_die            ... bench:     51569 ns/iter (+/- 6169)

4 threads

test bench_fibb_steal     ... bench:   2318548 ns/iter (+/- 516592)
test chain_10_use_die     ... bench:    148295 ns/iter (+/- 12029)
test chain_10_wait        ... bench:    119859 ns/iter (+/- 39196)
test chain_1_000_use_die  ... bench:    474476 ns/iter (+/- 89795)
test chain_1_000_wait     ... bench:    591176 ns/iter (+/- 164828)
test fanout_1_000         ... bench:  10284883 ns/iter (+/- 1993024)
test repeat_100_x_100     ... bench:   2194172 ns/iter (+/- 2243956)
test repeat_1_000         ... bench:   1203489 ns/iter (+/- 186731)
test repeat_1_000_x_1_000 ... bench: 180651629 ns/iter (+/- 31147220)
test start_die            ... bench:    141690 ns/iter (+/- 10331)

12 threads

test bench_fibb_steal     ... bench:   4266370 ns/iter (+/- 1680482)
test chain_10_use_die     ... bench:    782393 ns/iter (+/- 2540535)
test chain_10_wait        ... bench:    178198 ns/iter (+/- 32233)
test chain_1_000_use_die  ... bench:    774855 ns/iter (+/- 1612068)
test chain_1_000_wait     ... bench:    704695 ns/iter (+/- 196897)
test fanout_1_000         ... bench:  18206514 ns/iter (+/- 4213723)
test repeat_100_x_100     ... bench:   1432300 ns/iter (+/- 99255)
test repeat_1_000         ... bench:   1127044 ns/iter (+/- 462414)
test repeat_1_000_x_1_000 ... bench: 111746427 ns/iter (+/- 8963304)
test start_die            ... bench:   1875302 ns/iter (+/- 2491521)

A few of the tests are basically benchmarks of spawning threads start_die, chain_10_use_die for example.

It worries me that bench_fibb_steal gets worse as threads are added (it should be very parallel). And repeat_1_000_x_1_000 is at best a 3 times increase.