tree 16268a9f2714ea729d324124f16b9c81d1ae6692
parent 739f13383791847fd4b0a1eab7e333b5780be039
author Austin Clements <austin@google.com> 1438699529 -0400
committer Austin Clements <austin@google.com> 1442254540 +0000

runtime: split marking of span roots into 128 subtasks

Marking of span roots can represent a significant fraction of the time
spent in mark termination. Simply traversing the span list takes about
1ms per GB of heap and if there are a large number of finalizers (for
example, for network connections), it may take much longer.

Improve the situation by splitting the span scan into 128 subtasks
that can be executed in parallel and load balanced by the markroots
parallel for. This lets the GC balance this job across the Ps.

A better solution is to do this during concurrent mark, or to improve
it algorithmically, but this is a simple change with a lot of bang for
the buck.

This was suggested by Rhys Hiltner.

Updates #11485.

Change-Id: I8b281adf0ba827064e154a1b6cc32d4d8031c03c
Reviewed-on: https://go-review.googlesource.com/13112
Reviewed-by: Keith Randall <khr@golang.org>