1848278 - Make permanent atom set extensible by embedder

Status: ASSIGNED

(Core :: JavaScript Engine, task, P3)

Description

[Tooru Fujisawa [:arai]]

In order to avoid atomization in performance-critical path in Gecko, we could:

• expose the WellKnownAtomId to embedding and provide API to convert it to JSAtom and JS::PropertyKey
  • also extend JSPropertySpec and JSFunctionSpec so that WellKnownAtomId can be used there (bug 1847677)
• provide a way to extend the permanent atom set, and allow accessing it with extended-WellKnownAtomId-like index, so that gecko's static atoms can be converted into JSAtom with simple pointer calculation

Comment 1

[Tooru Fujisawa [:arai]]

Here's the summary of atomization that performed during startup (5 seconds after initialzing SpiderMonkey's permanent atoms).

1.1. new profile, newtab page, parent process

NOTE: parent process uses 4 runtimes, which shares cx->staticStrings() and cx->permanentAtoms(), but not cx->atoms(). which results in creating JSAtom for same content at most 4 times.

	count	unique atoms
total atomization	75867	60156
found in cx->staticStrings()	7257 (9.5 %) (*1)	187 (0.3 %)
found in cx->permanentAtoms()	2022 (2.6 %) (*2)	634 (1.0 %)
found in cx->atoms()	979 (1.2 %)	971 (1.6 %)
found in cx->atoms(): exists in gecko atoms	170 (0.2 %) (*3)	168 (0.2 %)
found in cx->atoms(): exists in binding properties	392 (0.5 %) (*5)	385 (0.6 %)
found in cx->atoms(): exists in either	398 (0.5 %)	391 (0.6 %)
new JSAtom	65609 (86.4 %)	59346 (98.6 %)
new JSAtom: exists in gecko atoms	1072 (1.4 %) (*3)	706 (1.1 %) (*3, *4)
new JSAtom: exists in binding properties	5881 (7.7 %) (*5)	3697 (6.1 %) (*5, *6)
new JSAtom: exists in either	6190 (8.1 %)	3952 (6.5 %)

• (*1) 9.5% of atomization can be replaced with cx->staticStrings() access
• (*2) 2.6% of atomization can be replaced with WellKnownAtomId
• if all gecko atoms are added to well-known:
  • (*3) 0.5% (0.2 + 1.4 - 1.1) of atomization can be skipped
  • (*4) 1.1% of atomization can be performed during initialization, which helps locality, and also can skip length and hash calculation
• if all WebIDL properties are added to well-known:
  • (*5) 2.1% (0.5 + 7.7 - 6.1) of atomization can be skipped
  • (*6) 6.1% of atomization can be performed during initialization, which helps locality, and also can skip length and hash calculation

Exposing WellKnownAtomId (bug 1848322) will allow (*2).
If we also expose static strings, (*1) become available.
The effect of this bug (*3 ~ *6) depends on the set of the extension, but at least using the gecko-atom seems to be simple enough (WIP patch).

If all of the above is done, this will affect 13~20% of the atomization.

1.2. new profile, newtab page, content process

	count	unique atoms
total atomization	33172	15535
found in cx->staticStrings()	918 (2.7 %)	161 (1.0 %)
found in cx->permanentAtoms()	1126 (3.3 %)	371 (2.3 %)
found in cx->atoms()	16125 (48.6 %)	11199 (72.0 %)
found in cx->atoms(): exists in gecko atoms	1040 (3.1 %)	468 (3.0 %)
found in cx->atoms(): exists in binding properties	3443 (10.3 %)	2024 (13.0 %)
found in cx->atoms(): exists in either	3581 (10.7 %)	2128 (13.6 %)
new JSAtom	15003 (45.2 %)	15003 (96.5 %)
new JSAtom: exists in gecko atoms	518 (1.5 %)	518 (3.3 %)
new JSAtom: exists in binding properties	2461 (7.4 %)	2461 (15.8 %)
new JSAtom: exists in either	2588 (7.8 %)	2588 (16.6 %)

In this case, this will affect 10~24% of the atomization.

2.1. session restore, YouTube top, parent process

	count	unique atoms
total atomization	78507	60432
found in cx->staticStrings()	13385 (17.0 %)	391 (0.6 %)
found in cx->permanentAtoms()	1555 (1.9 %)	625 (1.0 %)
found in cx->atoms()	902 (1.1 %)	897 (1.4 %)
found in cx->atoms(): exists in gecko atoms	168 (0.2 %)	167 (0.2 %)
found in cx->atoms(): exists in binding properties	384 (0.4 %)	379 (0.6 %)
found in cx->atoms(): exists in either	390 (0.4 %)	385 (0.6 %)
new JSAtom	62665 (79.8 %)	59419 (98.3 %)
new JSAtom: exists in gecko atoms	924 (1.1 %)	710 (1.1 %)
new JSAtom: exists in binding properties	4864 (6.1 %)	3729 (6.1 %)
new JSAtom: exists in either	5147 (6.5 %)	3980 (6.5 %)

In this case, this will affect 20~25% of the atomization.

2.2. session restore, YouTube top, content process

	count	unique atoms
total atomization	91253	87052
found in cx->staticStrings()	902 (0.9 %)	186 (0.2 %)
found in cx->permanentAtoms()	962 (1.0 %)	554 (0.6 %)
found in cx->atoms()	3077 (3.3 %)	2374 (2.7 %)
found in cx->atoms(): exists in gecko atoms	505 (0.5 %)	345 (0.3 %)
found in cx->atoms(): exists in binding properties	1346 (1.4 %)	959 (1.1 %)
found in cx->atoms(): exists in either	1405 (1.5 %)	1016 (1.1 %)
new JSAtom	86312 (94.5 %)	86312 (99.1 %)
new JSAtom: exists in gecko atoms	822 (0.9 %)	822 (0.9 %)
new JSAtom: exists in binding properties	3451 (3.7 %)	3451 (3.9 %)
new JSAtom: exists in either	3795 (4.1 %)	3795 (4.3 %)

In this case, this will affect 3~7% of the atomization.

Comment 2

[Tooru Fujisawa [:arai]]

Attachment: WIP: Bug 1848278 - Add extended known atom and related API. r?jandem!,bthrall!