1354817 - IonMonkey: ogv.js pthreads perf is comparatively slow

Status: NEW

(Core :: JavaScript Engine: JIT, defect, P3)

Description

[Alon Zakai (:azakai)]

As reported at https://brionv.com/log/2017/04/06/ogv-js-1-4-0-released/

> Experimental multithreaded versions of the VP8 and VP9 decoders are included, which can use up to 4 CPU cores to significantly increase speed on suitably encoded files (using the -slices option in ffmpeg for VP8, or -tile_columns for VP9). This works reasonably well in Safari and Chrome on Mac or Windows desktops; there are performance problems in Firefox due to deoptimization of the multithreaded code.

and link to test at

https://twitter.com/brionv/status/850375796157894658

With JIT_OPTION_asmJSAtomicsEnable=true things are much faster, as expected, but what is less obvious is why without that (i.e. in non-asm.js mode) Firefox does worse than Safari and Chrome.