Measure per-taskgroup actual CPU time in addition to scheduler ticks

Author: knz

src/runtime/proc.go

@@ -2537,6 +2537,8 @@ func execute(gp *g, inheritTime bool) {
 		_g_.m.p.ptr().schedtick++
 	}
 	// BEGIN - CockroachDB tweaks
+	// Accounting for the new G, the one we're scheduling into.
+	gp.lastSchedTime = nanotime()
 	if gp.taskGroupCtx != nil {
 		atomic.Xadd64(&gp.taskGroupCtx.schedtick, 1)
 	}
@@ -3185,6 +3187,15 @@ top:
 func dropg() {
 	_g_ := getg()
 
+	// BEGIN - CockroachDB tweaks
+	// Accounting for the past G, the one we're scheduling away from.
+	if _g_.m.curg != nil && _g_.m.curg.taskGroupCtx != nil {
+		endTickTime := nanotime()
+		lastTime := _g_.m.curg.lastSchedTime
+		atomic.Xadd64(&_g_.m.curg.taskGroupCtx.nanos, endTickTime-lastTime)
+	}
+	// END - CockroachDB tweaks
+
 	setMNoWB(&_g_.m.curg.m, nil)
 	setGNoWB(&_g_.m.curg, nil)
 }

src/runtime/runtime2.go

@@ -474,6 +474,10 @@ type g struct {
 	// BEGIN - CockroachDB tweaks
 	taskGroupId  int64 // inherited goroutine task group ID. Typically set from the task group root's own goroutine ID via SetGoroutineGroupID(GetGID()).
 	taskGroupCtx *t    // inherited task group context.
+
+	// lastSchedTime is the nanotime of the last time a goroutine
+	// was scheduled into a P.
+	lastSchedTime int64
 	// END - CockroachDB tweaks
 
 	// Per-G GC state

src/runtime/task_group.go

@@ -10,6 +10,7 @@ import "runtime/internal/atomic"
 
 type t struct {
 	schedtick uint64 // incremented atomically on every scheduler call
+	nanos     uint64 // cumulative slices of CPU time used by the task group, in nanoseconds
 }
 
 // defaulTaskGroupCtx is used for top level goroutines without a task group yet.
@@ -35,3 +36,10 @@ func GetInternalTaskGroupSchedTicks(taskGroup InternalTaskGroup) uint64 {
 	tg := (*t)(taskGroup)
 	return atomic.Load64(&tg.schedtick)
 }
+
+// GetInternalTaskGroupNanos retrieves the number of CPU nanoseconds used by
+// all goroutines in the given task group.
+func GetInternalTaskGroupNanos(taskGroup InternalTaskGroup) uint64 {
+	tg := (*t)(taskGroup)
+	return atomic.Load64(&tg.nanos)
+}