Hi all,
I am the maintainer of a plotting library, plotters. And I was discussing some performance issue on Github with others. And I realized one thing that is quite shocking to me. It seems two "?" operator makes the crate 50% slower.
Here's the benchmark
Local repo:
test sine_640_480 ... bench: 4,188,667 ns/iter (+/- 338,945)
test sine_640_480_2_horizontal_subgraphs_draw_both ... bench: 4,609,418 ns/iter (+/- 407,366)
test sine_640_480_2_horizontal_subgraphs_draw_one ... bench: 2,298,113 ns/iter (+/- 461,527)
test sine_640_480_2_horizontal_subgraphs_fake_blit ... bench: 270,355 ns/iter (+/- 53,794)
0.2.8:
test sine_640_480 ... bench: 7,277,665 ns/iter (+/- 3,636,985)
test sine_640_480_2_horizontal_subgraphs_draw_both ... bench: 8,129,140 ns/iter (+/- 937,515)
test sine_640_480_2_horizontal_subgraphs_draw_one ... bench: 4,303,821 ns/iter (+/- 255,423)
test sine_640_480_2_horizontal_subgraphs_fake_blit ... bench: 288,119 ns/iter (+/- 102,912)
The code I changed to make the difference is Change the line rasterizer not using "?" to handle error. result 50% … · plotters-rs/plotters@0571607 · GitHub
It seems the into_result uses 50% of the CPU time in total.
Is anybody know what is going on?
The link to the original issue in github: [BUG] Investigate the performance overhead of result types · Issue #58 · plotters-rs/plotters · GitHub
The CPU Profiler result: https://user-images.githubusercontent.com/3023614/66969933-c4b4b700-f048-11e9-9456-780b91bb7f8b.png
And I checked the Try::into_result impl for Result<T,E>, I don't know why this function so expensive at all. result.rs - source