1670328 - Limit SwCompositeThread overhead

Status: RESOLVED FIXED

(Core :: Graphics: WebRender, enhancement, P3)

Description

[Lee Salzman [:lsalzman]]

Currently every SwCompositor has a SwCompositeThread associated with it. Most of these threads are parked and not doing much though when their respective windows are not active. We might want to investigate stuffing these into a limited size thread-pool.

Alternatively, we might want to just limit the size of the SwCompositeThread's stack, since all the thread does is call Composite in a loop, and a large stack for each thread of these threads is wasteful.

Comment 1

[Lee Salzman [:lsalzman]]

Attachment: Bug 1670328 - remove crossbeam usage from SwCompositor. r?mattwoodrow

We seem to be spending a significant amount of time inside crossbeam channels
sending jobs across. Sending multiple bands for a given job tends to relock the
channel multiple times when ideally we only want to queue the job once, or lock
the channel once (neither of which we can conveniently do with crossbeam). To
alleviate this, I've implemented a more custom solution with a mutexed VecDeque
and some Condvars. I also made compositor threads spawn from WR thread pool to
make thread termination a bit saner such that threads are spawned when
compositing starts and terminate when compositing is done.

Comment 2

[Lee Salzman [:lsalzman]]

Attachment: Bug 1670328 - use SwCompositeGraphNodeRef wrapper for cleaner node mutation. r?mattwoodrow

Depends on D96520

Comment 3

[Lee Salzman [:lsalzman]]

Attachment: Bug 1670328 - reduce stack size for SwComposite threads. r?mattwoodrow

There appears to be a substantial overhead for trying to wake cold threads
from a thread pool (especially with rayon), so for now let's leave the existing
thread spawning in place, but reduce the stack size for individual threads.
Since these threads only call into SWGL's composite routines and do little else,
there isn't much harm in having a small stack size.

Depends on D96732

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/e111e9ce3754
remove crossbeam usage from SwCompositor. r=mattwoodrow
https://hg.mozilla.org/integration/autoland/rev/8d47e408c578
use SwCompositeGraphNodeRef wrapper for cleaner node mutation. r=mattwoodrow
https://hg.mozilla.org/integration/autoland/rev/fd235fdcca9e
reduce stack size for SwComposite threads. r=mattwoodrow

Comment 5

[Natalia Csoregi [:nataliaCs]]

https://hg.mozilla.org/mozilla-central/rev/e111e9ce3754
https://hg.mozilla.org/mozilla-central/rev/8d47e408c578
https://hg.mozilla.org/mozilla-central/rev/fd235fdcca9e