Bug 200444 – High number of cache miss on localTimeOffset

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Caio Lima]

There are cases with a high number of cache miss on `localTimeOffset` while using "https://www.messenger.com". From profiling information collected during usage of ~10 minutes, there were ~3520 cache miss and 54 cache hit. The profiling was collected during conversation in 2 chats.

[Caio Lima]

Also the problem happens when applications call `gregorianDateTimeToMS` and `msToGregorianDateTime` intercalated and `inputTimeType ==  WTF::LocalTime` in both functions. The issue happens because `msToGregorianDateTime` calls `localTimeOffset` with `WTF::UTCTime` and force a cache reset.

[Caio Lima]

Created attachment 375548 [details]
WIP - Patch

[Caio Lima]

Created attachment 375625 [details]
Patch

[Geoffrey Garen]

** The following JSC stress test failures have been introduced:
	mozilla-tests.yaml/js1_5/Array/regress-101964.js.mozilla

[Geoffrey Garen]

Comment on attachment 375625 [details]
Patch

Patch looks correct -- can you run the JSC tests locally and see if you reproduce that failure?

Also, it would be nice, in a follow-up, to remove callers that use WTF::LocalTime. The input to this function is supposed to be UTC time exclusively.

[Caio Lima]

Thx a lot for the review!

(In reply to Geoffrey Garen from comment #4)
> ** The following JSC stress test failures have been introduced:
> 	mozilla-tests.yaml/js1_5/Array/regress-101964.js.mozilla

Since last month, this test is failing sometimes. It fails more often on MIPS bots, but I saw it failing on jsc EWS in a couple of patches I've sent last week. We tried to reproduce the fail locally using our MIPS bots, but it seems to happen only when running stress tests and in a very specific case we didn't identify yet. I personally couldn't reproduce it on macOS so far.
Anyway, I'm running tests locally before commiting it.

[Caio Lima]

Comment on attachment 375625 [details]
Patch

Failure doesn't see related. I ran Debug and Relase mode locally and got no error.

[WebKit Commit Bot]

Comment on attachment 375625 [details]
Patch

Clearing flags on attachment: 375625

Committed r248363: <https://trac.webkit.org/changeset/248363>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.

[Radar WebKit Bug Importer]

<rdar://problem/54029582>

[Caio Lima]

(In reply to Geoffrey Garen from comment #5)
> Comment on attachment 375625 [details]
> Patch
> 
> Patch looks correct -- can you run the JSC tests locally and see if you
> reproduce that failure?
> 
> Also, it would be nice, in a follow-up, to remove callers that use
> WTF::LocalTime. The input to this function is supposed to be UTC time
> exclusively.

Just for the record, this is the bug where `WTF::TimeType` was introduced. https://bugs.webkit.org/show_bug.cgi?id=130967