1161726 - Speed up minor collections

Status: RESOLVED FIXED

(Core :: JavaScript: GC, defect)

Description

[Terrence Cole [:terrence]]

Attachment: 18_custom_marking_for_nursery-v0.diff

TL;DR
╰> octane goes from 41859 -> 42414
╰> octane has ~15% fewer nursery collections taking >500us

The current patch is very simple: it moves the existing nursery collection code to Marking.cpp, uses a new JSTracer subclass to avoid the indirect call overhead, and specializes StoreBuffer::*::mark to skip DispatchToTracer. Microbenchmarks show that traversing a store buffer is roughly 2x faster with the patch applied.

Further work is needed here: I want to experiment with using a mark stack instead of an inline list to see if I can eek out any further improvements. Also, we should be able to share some of this code with processMarkStackTop, somehow.

https://treeherder.mozilla.org/#/jobs?repo=try&revision=5db59d84dabf

Comment 1

[Terrence Cole [:terrence]]

Attachment: 18_custom_marking_for_nursery-v0.diff

Missing a qref.

Comment 2

[Jon Coppeard (:jonco)]

Comment on attachment 8601696 [details] [diff] [review]
18_custom_marking_for_nursery-v0.diff

Review of attachment 8601696 [details] [diff] [review]:
-----------------------------------------------------------------

This is great!

::: js/src/gc/Nursery-inl.h
@@ +21,5 @@
>      MOZ_ASSERT(isInside((void*)*ref));
>      const gc::RelocationOverlay* overlay = reinterpret_cast<const gc::RelocationOverlay*>(*ref);
>      if (!overlay->isForwarded())
>          return false;
>      /* This static cast from Cell* restricts T to valid (GC thing) types. */

This comment needs updating/removing.

Comment 3

[Terrence Cole [:terrence]]

https://treeherder.mozilla.org/#/jobs?repo=try&revision=5db59d84dabf

Comment 4

[Pulsebot]

https://hg.mozilla.org/integration/mozilla-inbound/rev/455fb7de9f84

Comment 5

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/455fb7de9f84

Comment 6

[Daniel Holbert [:dholbert]]

Comment on attachment 8601696 [details] [diff] [review]
18_custom_marking_for_nursery-v0.diff

>--- a/js/src/gc/Nursery.cpp
>+++ b/js/src/gc/Nursery.cpp
[...]
>-struct TenureCount
>+js::TenuringTracer::TenuringTracer(JSRuntime* rt, Nursery* nursery)
>+  : JSTracer(rt, JSTracer::TracerKindTag::Tenuring, TraceWeakMapKeysValues)
>+  , nursery_(*nursery)
>+  , tenuredSize(0)
>+  , head(nullptr)
>+  , tail(&head)
>+  , savedRuntimeNeedBarrier(rt->needsIncrementalBarrier())
>+#ifdef JS_GC_ZEAL
>+  , verifyingPostBarriers(nullptr)
>+#endif
> {

This "verifyingPostBarriers" initialization causes Werror build bustage for me, locally (with clang 3.7).

The build warning (error) is:

> js/src/gc/Nursery.cpp:383:27: error: implicit conversion of nullptr constant to 'bool' [-Werror,-Wnull-conversion]
>   , verifyingPostBarriers(nullptr)
>                         ~^~~~~~~
> 1 error generated.

Terrence, should this be s/nullptr/false/? Could you push a followup to fix?

Comment 7

[Daniel Holbert [:dholbert]]

Ah, terrence says on IRC that bug 1161353 (which just landed) will address comment 6.