1823622 - Some small parallel marking improvements

Status: RESOLVED FIXED

(Core :: JavaScript: GC, task, P3)

Comment 1

[Jon Coppeard (:jonco)]

Attachment: Bug 1823622 - Part 1: Remove unused condition variable r?sfink

This used to be used by an earlier iteration of the code but it seems I forgot
to remove it.

Comment 2

[Jon Coppeard (:jonco)]

Attachment: Bug 1823622 - Part 2: Refine parallel marking telemetry to exclude wait times r?sfink

There are three measurements made for parallel mark threads: 1) total time, 2)
marking time and 3) waiting time (when the thread is blocked on a condition
variable).

When calculating utilization we want to use the time the thread was running so
we should exclude waiting time. When calculating the speedup over single
threaded marking we want to use the time the thread spent marking.

Depends on D173127

Comment 3

[Jon Coppeard (:jonco)]

Attachment: Bug 1823622 - Part 3: Lower the threshold at which we calculate mark rate telemetry r?sfink

We don't calculate this when marking is quick to exclude unreliable results
when the denominator of the calculation is very small. However we can mark in
less than 1 millisecond for small heaps with parallel marking, so this reduces
the threshold to 1 microsecond.

Depends on D173128

Comment 4

[Jon Coppeard (:jonco)]

Attachment: Bug 1823622 - Part 4: Make SliceBudget's interrupt word a relaxed atomic r?sfink

Since this can get checked by all marking threads it's not optimal to have this
as a sequentially consistent atomic as this will cause cache traffic every time
it's read.

We should be able to make this a relaxed atomic without observable difference
to interruptible GC.

Depends on D173129

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/4c55048434e2
Part 1: Remove unused condition variable r=sfink
https://hg.mozilla.org/integration/autoland/rev/d6d6b895d730
Part 2: Refine parallel marking telemetry to exclude wait times r=sfink
https://hg.mozilla.org/integration/autoland/rev/2d6a608863af
Part 3: Lower the threshold at which we calculate mark rate telemetry r=sfink
https://hg.mozilla.org/integration/autoland/rev/b2be266873a2
Part 4: Make SliceBudget's interrupt word a relaxed atomic r=sfink

Comment 6

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/4c55048434e2
https://hg.mozilla.org/mozilla-central/rev/d6d6b895d730
https://hg.mozilla.org/mozilla-central/rev/2d6a608863af
https://hg.mozilla.org/mozilla-central/rev/b2be266873a2