Bug 165910 – Make the collector's fixpoint smart about scheduling work

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Filip Pizlo]

The GC currently scans a bunch of things in each fixpoint iteration.  It will sometimes do many fixpoint iterations.  I suspect that when it does have to perform multiple fixpoint iterations, it's because some specific part of the fixpoint is being very needy.  This implies that we can dramatically improve the fixpoint's performance using traditional fixpoint optimization tricks.

[Filip Pizlo]

I'm imagining that each of the phases of the weak fixpoint would be put into a SharedTask or some even smarter object, and then we'd be able to write some scheduler that runs them in an order that reduces the average number of executions.

[Filip Pizlo]

*** Bug 165963 has been marked as a duplicate of this bug. ***

[Filip Pizlo]

I was originally thinking that in bug 165963, I would implement the infrastructure that's needed to intelligently schedule work and then in this bug I would use that infrastructure to get an optimization. I ended up doing both of those things in bug 165963.

[Filip Pizlo]

Created attachment 298310 [details]
possible patch

[Filip Pizlo]

Created attachment 298316 [details]
the patch

[WebKit Commit Bot]

Attachment 298316 [details] did not pass style-queue:


ERROR: Source/JavaScriptCore/heap/MarkingConstraintSet.cpp:201:  An else statement can be removed when the prior "if" concludes with a return, break, continue or goto statement.  [readability/control_flow] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:37:  Code inside a namespace should not be indented.  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:37:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:38:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:39:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:40:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:49:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:50:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:51:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:52:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:53:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
Total errors found: 11 in 27 files


If any of these errors are false positives, please file a bug against check-webkit-style.

[Filip Pizlo]

Created attachment 298320 [details]
the patch

[WebKit Commit Bot]

Attachment 298320 [details] did not pass style-queue:


ERROR: Source/JavaScriptCore/heap/MarkingConstraintSet.cpp:201:  An else statement can be removed when the prior "if" concludes with a return, break, continue or goto statement.  [readability/control_flow] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:37:  Code inside a namespace should not be indented.  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:37:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:38:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:39:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:40:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:49:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:50:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:51:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:52:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:53:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
Total errors found: 11 in 27 files


If any of these errors are false positives, please file a bug against check-webkit-style.

[Filip Pizlo]

Created attachment 298321 [details]
the patch

[WebKit Commit Bot]

Attachment 298321 [details] did not pass style-queue:


ERROR: Source/JavaScriptCore/heap/MarkingConstraintSet.cpp:201:  An else statement can be removed when the prior "if" concludes with a return, break, continue or goto statement.  [readability/control_flow] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:37:  Code inside a namespace should not be indented.  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:37:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:38:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:39:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:40:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:49:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:50:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:51:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:52:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
ERROR: Source/JavaScriptCore/heap/MarkingConstraint.cpp:53:  Wrong number of spaces before statement. (expected: 8)  [whitespace/indent] [4]
Total errors found: 11 in 27 files


If any of these errors are false positives, please file a bug against check-webkit-style.

[Keith Miller]

Comment on attachment 298321 [details]
the patch

View in context: https://bugs.webkit.org/attachment.cgi?id=298321&action=review

r=me with some minor comments.

> Source/JavaScriptCore/heap/MarkingConstraintSet.cpp:124
> +void MarkingConstraintSet::add(
> +    std::unique_ptr<MarkingConstraint> constraint)

Nit, put this on one line.

> Source/JavaScriptCore/heap/SpaceTimeMutatorScheduler.cpp:2
> + * Copyright (C) 2016 Apple Inc. All rights reserved.

2017

> Source/JavaScriptCore/heap/SpaceTimeMutatorScheduler.h:2
> + * Copyright (C) 2016 Apple Inc. All rights reserved.

2017

[Filip Pizlo]

(In reply to comment #11)
> Comment on attachment 298321 [details]
> the patch
> 
> View in context:
> https://bugs.webkit.org/attachment.cgi?id=298321&action=review
> 
> r=me with some minor comments.
> 
> > Source/JavaScriptCore/heap/MarkingConstraintSet.cpp:124
> > +void MarkingConstraintSet::add(
> > +    std::unique_ptr<MarkingConstraint> constraint)
> 
> Nit, put this on one line.

Done.

> 
> > Source/JavaScriptCore/heap/SpaceTimeMutatorScheduler.cpp:2
> > + * Copyright (C) 2016 Apple Inc. All rights reserved.
> 
> 2017

You're commenting on the pseudofile that the patch is showing you.  In fact, SpaceTimeMutatorScheduler.cpp:2 is:

 * Copyright (C) 2016-2017 Apple Inc. All rights reserved.

> 
> > Source/JavaScriptCore/heap/SpaceTimeMutatorScheduler.h:2
> > + * Copyright (C) 2016 Apple Inc. All rights reserved.
> 
> 2017

Ditto.

[Filip Pizlo]

Landed in https://trac.webkit.org/changeset/210521

[Filip Pizlo]

Fixed cloop in https://trac.webkit.org/changeset/210530