internal/trace: add comment for stable sort

As per comments in cl/11834.

Change-Id: I285536b882fa9496e15d77d0d4c16ee913aca581
Reviewed-on: https://go-review.googlesource.com/11861
Reviewed-by: Daniel Theophanes <kardianos@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

diff --git a/src/internal/trace/parser.go b/src/internal/trace/parser.go
index 1117b18e4769b7103a4ef4ec48c52ba32719b946..ece5bc188de51c27d8fbd6b5b1c2e4cfea7cfbfa 100644 (file)
--- a/src/internal/trace/parser.go
+++ b/src/internal/trace/parser.go
@@ -254,6 +254,8 @@ func parseEvents(rawEvents []rawEvent) (events []*Event, err error) {
        }
 
        // Sort by time and translate cpu ticks to real time.
+       // Use stable sort because adjacent events in a batch can have the same timestamp
+       // (this was observed on some VMs).
        sort.Stable(eventList(events))
        if ticksPerSec == 0 {
                err = fmt.Errorf("no EvFrequency event")