cmd/trace: avoid emitting traceview slice with 0 duration

The trace viewer interprets the slice as a non-terminating
time interval which is quite opposit to what trace records indicate
(i.e., almostly immediately terminating time interval).
As observed in the issue #24663 this can result in quite misleading
visualization of the trace.

Work around the trace viewer's issue by setting a small value
(0.0001usec) as the duration if the time interval is not positive.

Change-Id: I1c2aac135c194d0717f5c01a98ca60ffb14ef45c
Reviewed-on: https://go-review.googlesource.com/104716
Reviewed-by: Heschi Kreinick <heschi@google.com>

diff --git a/src/cmd/trace/trace.go b/src/cmd/trace/trace.go
index 12d8dec7539245be52a703bb38790f1f2fd6ffa9..ecc7c3f9c92181e97f837c769790fbaf1bc656ce 100644 (file)
--- a/src/cmd/trace/trace.go
+++ b/src/cmd/trace/trace.go
@@ -815,11 +815,18 @@ func (ctx *traceContext) proc(ev *trace.Event) uint64 {
 }
 
 func (ctx *traceContext) emitSlice(ev *trace.Event, name string) *ViewerEvent {
+       // If ViewerEvent.Dur is not a positive value,
+       // trace viewer handles it as a non-terminating time interval.
+       // Avoid it by setting the field with a small value.
+       durationUsec := ctx.time(ev.Link) - ctx.time(ev)
+       if ev.Link.Ts-ev.Ts <= 0 {
+               durationUsec = 0.0001 // 0.1 nanoseconds
+       }
        sl := &ViewerEvent{
                Name:     name,
                Phase:    "X",
                Time:     ctx.time(ev),
-               Dur:      ctx.time(ev.Link) - ctx.time(ev),
+               Dur:      durationUsec,
                Tid:      ctx.proc(ev),
                Stack:    ctx.stack(ev.Stk),
                EndStack: ctx.stack(ev.Link.Stk),