Brendan Eich [:brendan] Reporter
	Description • 15 years ago

Regarding bug 533254 and its testcase, which has some apparent deadwood that turns out to be required to reproduce the assertbotch without that bug's patch:

[3:59pm] brendan: indeed, property cache collisions
[3:59pm] jorendorff: yep, got your message <brendan> yes, propcache.stats differs -- yuck
[4:00pm] brendan: http://pastebin.mozilla.org/689381
[4:00pm] brendan: full analysis
[4:00pm] brendan: the ^ hurts in PROPERTY_CACHE_HASH
[4:00pm] brendan: could use + to avoid "binary subtraction" effect
[4:00pm] brendan: the intermediates i dumped in gdb nicely differ by the additive inverse of the shape delta (shapes go up, kpc intermediate hash goes down, by 2)
[4:01pm] brendan: stupid xor!
[4:01pm] jorendorff: amazing! hang on
[4:09pm] jorendorff: sorry, had to check the bitmath to believe it; i've never seen it happen before
[4:10pm] jorendorff: well any significant improvement in hit rate has to be more important than the difference between a xor instruction and an add
[4:11pm] jorendorff: the thing is, at least the current approach shuffles the bits
[4:11pm] jorendorff: if we add instead, we might end up having some idiom that triggers worst-case behavior.
[4:12pm] brendan: yes, it may be we just want the low pc bits
[4:12pm] brendan: for these setprop/initprop strides along the cache, anyway
[4:14pm] jorendorff: ok, i think i would try + first... wow

Measure twice, cut once... filing this to remind myself to see what can be done. Feel free to steal this bug.

/be

	Brendan Eich [:brendan] Reporter
	Comment 1 • 15 years ago

Jason kindly agreed to take ownership of this bug.

/be

	Brendan Eich [:brendan] Reporter
	Comment 2 • 15 years ago

I would be happy with /tmp/propcache.stats wins for SunSpider tests, maybe v8, and no perf regression according to our infrastructure. More exhaustive testing would be gravy; not sure how to get it though. Instrument the cache keys probed for in a real Firefox multi-tab session and play them back with old and new algs?

/be

	Sylvestre Ledru [:Sylvestre]
	Comment 3 • 6 years ago

Moving to p3 because no activity for at least 1 year(s).
See https://github.com/mozilla/bug-handling/blob/master/policy/triage-bugzilla.md#how-do-you-triage for more information

	Jan de Mooij [:jandem]
	Comment 4 • 6 years ago

Property cache was removed 5+ years ago.