Closed Bug 827392 Opened 7 years ago Closed 2 years ago
Skippable pause times
We've moved a lot of CC work into ForgetSkippable, which is good, but now ForgetSkippable pauses can be as long as CC pauses now, so we should investigate where the time is being spent, and figure out how to reduce that. My guess is that the longest pauses are in that first ForgetSkippable call after a GC, due to all the UnmarkGray cleanup we do. If that's the case, then we should figure out how we can make more of the obviously-live JS get marked black instead of gray. One way to do this would be to take a snapshot of the JS heap before and after the ForgetSkippable call, and look at the objects that changed color.
Usually max forgetskippable time is significantly lower than CC. Median time is 3ms. The first 2 forgetSkippables after GC are the most important and yeah, I'd assume the first one is the slowest one.
As expected, most of the time (but not all) was being spent in nsCCUncollectableMarker::Observe. Here's a patch to add some basic timing. Here are some results for those taking more than 1ms: cc: MarkWindowList mediator took 2302us cc: MarkWindowList watcher took 939us cc: AppShellService took 29us cc: xulCache took 1995us cc: CleanupJS took 2253us cc: TOTAL took 7564us cc: MarkWindowList mediator took 1046us cc: MarkWindowList watcher took 980us cc: AppShellService took 13us cc: xulCache took 89us cc: UnmarkSkippableJSHolders took 566us cc: TOTAL took 2719us cc: MarkWindowList mediator took 410us cc: MarkWindowList watcher took 58us cc: AppShellService took 34us cc: xulCache took 1136us cc: CleanupJS took 1171us cc: TOTAL took 2855us cc: MarkWindowList mediator took 360us cc: MarkWindowList watcher took 40us cc: AppShellService took 27us cc: xulCache took 1014us cc: CleanupJS took 1326us cc: TOTAL took 2811us cc: MarkWindowList mediator took 369us cc: MarkWindowList watcher took 53us cc: AppShellService took 29us cc: xulCache took 1784us cc: CleanupJS took 1155us cc: TOTAL took 3430us
I looked at XULCACHE first, as that is probably easier to fix. It has two parts, XBL and XUL. It seems to be mostly XBL, though if they tend to hold onto the same objects, then it will just be a matter of XBL going first. cc: MarkXBLInCCGeneration took 1119us cc: MarkXULInCCGeneration took 12us cc: xulCache took 1140us cc: MarkXBLInCCGeneration took 127us cc: MarkXULInCCGeneration took 7us cc: xulCache took 142us cc: MarkXBLInCCGeneration took 103us cc: MarkXULInCCGeneration took 7us cc: xulCache took 119us cc: MarkXBLInCCGeneration took 854us cc: MarkXULInCCGeneration took 12us cc: xulCache took 876us
Detailed time spent in cleanupJS: cc: CleanupJS:UnmarkGrayJSListeners took 619us cc: CleanupJS:MarkMessageManagers took 134us cc: CleanupJS:UnmarkGrayStrongObservers took 323us
Quite a few of these must happen right after MarkWindowList* so that documents are in CC generation. XUL/XBL cache and observer stuff marking doesn't need that, and could happen (perhaps async) right after GC, or even during GC.
Bug 827534 eliminates most of the xulCache problems. We could do a similar thing for the observer stuff, make it marked black instead of relying on unmarkGray. That would reduce the amount of work we do, in addition to reducing pauses.
Summary: Investigate time spent in ForgetSkippable → Reduce time spent in ForgetSkippable
Depends on: 1097302
Summary: Reduce time spent in ForgetSkippable → Reduce ForgetSkippable pause times
This is probably good enough for now...
Status: NEW → RESOLVED
Closed: 2 years ago
Resolution: --- → FIXED
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