cmd/trace: label mark termination spans as such

Currently these are labeled "MARK", which was accurate in the STW
collector, but these really indicate mark termination now, since
marking happens for the full duration of the concurrent GC. Re-label
them as "MARK TERMINATION" to clarify this.

Change-Id: Ie98bd961195acde49598b4fa3f9e7d90d757c0a6
Reviewed-on: https://go-review.googlesource.com/30018Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

src/cmd/trace/trace.go

@@ -362,7 +362,7 @@ func generateTrace(params *traceParams) ViewerData {
 			if ctx.gtrace {
 				continue
 			}
-			ctx.emitSlice(ev, "MARK")
+			ctx.emitSlice(ev, "MARK TERMINATION")
 		case trace.EvGCScanDone:
 		case trace.EvGCSweepStart:
 			ctx.emitSlice(ev, "SWEEP")

src/internal/trace/parser.go

@@ -858,8 +858,8 @@ const (
 	EvProcStop       = 6  // stop of P [timestamp]
 	EvGCStart        = 7  // GC start [timestamp, seq, stack id]
 	EvGCDone         = 8  // GC done [timestamp]
-	EvGCScanStart    = 9  // GC scan start [timestamp]
-	EvGCScanDone     = 10 // GC scan done [timestamp]
+	EvGCScanStart    = 9  // GC mark termination start [timestamp]
+	EvGCScanDone     = 10 // GC mark termination done [timestamp]
 	EvGCSweepStart   = 11 // GC sweep start [timestamp, stack id]
 	EvGCSweepDone    = 12 // GC sweep done [timestamp]
 	EvGoCreate       = 13 // goroutine creation [timestamp, new goroutine id, new stack id, stack id]

src/runtime/trace.go

@@ -28,8 +28,8 @@ const (
 	traceEvProcStop       = 6  // stop of P [timestamp]
 	traceEvGCStart        = 7  // GC start [timestamp, seq, stack id]
 	traceEvGCDone         = 8  // GC done [timestamp]
-	traceEvGCScanStart    = 9  // GC scan start [timestamp]
-	traceEvGCScanDone     = 10 // GC scan done [timestamp]
+	traceEvGCScanStart    = 9  // GC mark termination start [timestamp]
+	traceEvGCScanDone     = 10 // GC mark termination done [timestamp]
 	traceEvGCSweepStart   = 11 // GC sweep start [timestamp, stack id]
 	traceEvGCSweepDone    = 12 // GC sweep done [timestamp]
 	traceEvGoCreate       = 13 // goroutine creation [timestamp, new goroutine id, new stack id, stack id]