runtime: track scan work performed during concurrent mark

This tracks the amount of scan work in terms of scanned pointers
during the concurrent mark phase. We'll use this information to
estimate scan work for the next cycle.

Currently this aggregates the work counter in gcWork and dispose
atomically aggregates this into a global work counter. dispose happens
relatively infrequently, so the contention on the global counter
should be low. If this turns out to be an issue, we can reduce the
number of disposes, and if it's still a problem, we can switch to
per-P counters.

Change-Id: Iac0364c466ee35fab781dbbbe7970a5f3c4e1fc1
Reviewed-on: https://go-review.googlesource.com/8832
Reviewed-by: Rick Hudson <rlh@golang.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/src/runtime/mgcwork.go b/src/runtime/mgcwork.go
index acd8e48309..fbe4d03adf 100644
--- a/src/runtime/mgcwork.go
+++ b/src/runtime/mgcwork.go
@@ -57,6 +57,10 @@ type gcWork struct {
 	// Bytes marked (blackened) on this gcWork. This is aggregated
 	// into work.bytesMarked by dispose.
 	bytesMarked uint64
+
+	// Scan work performed on this gcWork. This is aggregated into
+	// gcController by dispose.
+	scanWork int64
 }
 
 // initFromCache fetches work from this M's currentwbuf cache.
@@ -164,6 +168,10 @@ func (w *gcWork) dispose() {
 		xadd64(&work.bytesMarked, int64(w.bytesMarked))
 		w.bytesMarked = 0
 	}
+	if w.scanWork != 0 {
+		xaddint64(&gcController.scanWork, w.scanWork)
+		w.scanWork = 0
+	}
 }
 
 // disposeToCache returns any cached pointers to this M's currentwbuf.
@@ -181,6 +189,10 @@ func (w *gcWork) disposeToCache() {
 		xadd64(&work.bytesMarked, int64(w.bytesMarked))
 		w.bytesMarked = 0
 	}
+	if w.scanWork != 0 {
+		xaddint64(&gcController.scanWork, w.scanWork)
+		w.scanWork = 0
+	}
 }
 
 // balance moves some work that's cached in this gcWork back on the