933309 - GenerationalGC: fix performance on pdf.js

Status: RESOLVED WORKSFORME

(Core :: JavaScript Engine, defect)

Description

[Terrence Cole [:terrence]]

An initial look shows us spending over 1.5s in minor collection because of constant overflows of the generic store buffer. These appear to be for the DenseRange barriers for array_splice.

An initial look: the majority of these are sourced from an object in the nursery, so can simply be dropped. Checking before inserting reduces our total time in the minor GC down to <0.2s, an order of magnitude improvement: nice. This changes our score from on pdf.js from 7636 to 5040, a decrease in performance of -34%. It seems this test is too expensive and we need to do something more sophisticated.

This bug is for doing something more sophisticated, whatever that turns out to be.

Comment 1

[Terrence Cole [:terrence]]

Bug 990336 got us close to what we had pre-ggc, but there is still a bit more to do before we can claim parity.