doc/next: add section for Green Tea

Change-Id: I420e8d673e5d34d1b09c02b8bc84b890da42e320
Reviewed-on: https://go-review.googlesource.com/c/go/+/725662
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

diff --git a/doc/next/4-runtime.md b/doc/next/4-runtime.md
index 1f8e445e0b10dec62dbb8c5f06d35ece0db1cfdd..d8fcb8f9ee9fa764e8bf5686597a20baae0e0acd 100644 (file)
--- a/doc/next/4-runtime.md
+++ b/doc/next/4-runtime.md
@@ -1 +1,22 @@
 ## Runtime {#runtime}
+
+### New garbage collector
+
+The Green Tea garbage collector, previously available as an experiment in
+Go 1.25, is now enabled by default after incorporating feedback.
+
+This garbage collector’s design improves the performance of marking and
+scanning small objects through better locality and CPU scalability.
+Benchmark result vary, but we expect somewhere between a 10—40% reduction
+in garbage collection overhead in real-world programs that heavily use the
+garbage collector.
+Further improvements, on the order of 10% in garbage collection overhead,
+are expected when running on newer amd64-based CPU platforms (Intel Ice
+Lake or AMD Zen 4 and newer), as the garbage collector now leverages
+vector instructions for scanning small objects when possible.
+
+The new garbage collector may be disabled by setting
+`GOEXPERIMENT=nogreenteagc` at build time.
+This opt-out setting is expected to be removed in Go 1.27.
+If you disable the new garbage collector for any reason related to its
+performance or behavior, please [file an issue](/issue/new).