runtime: add 'next' flag to ready

Currently ready always puts the readied goroutine in runnext. We're
going to have to change this for some uses, so add a flag for whether
or not to use runnext.

For now we always pass true so this is a no-op change.

For #15706.

Change-Id: Iaa66d8355ccfe4bbe347570cc1b1878c70fa25df
Reviewed-on: https://go-review.googlesource.com/23171
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

src/runtime/mgc.go

@@ -1704,7 +1704,7 @@ func gcSweep(mode gcMode) {
 	lock(&sweep.lock)
 	if sweep.parked {
 		sweep.parked = false
-		ready(sweep.g, 0)
+		ready(sweep.g, 0, true)
 	}
 	unlock(&sweep.lock)
 	mProf_GC()

src/runtime/mgcmark.go

@@ -601,7 +601,7 @@ func gcFlushBgCredit(scanWork int64) {
 			gp.gcAssistBytes = 0
 			xgp := gp
 			gp = gp.schedlink.ptr()
-			ready(xgp, 0)
+			ready(xgp, 0, true)
 		} else {
 			// Partially satisfy this assist.
 			gp.gcAssistBytes += scanBytes

src/runtime/proc.go

@@ -273,7 +273,7 @@ func goparkunlock(lock *mutex, reason string, traceEv byte, traceskip int) {
 
 func goready(gp *g, traceskip int) {
 	systemstack(func() {
-		ready(gp, traceskip)
+		ready(gp, traceskip, true)
 	})
 }
 
@@ -533,7 +533,7 @@ func mcommoninit(mp *m) {
 }
 
 // Mark gp ready to run.
-func ready(gp *g, traceskip int) {
+func ready(gp *g, traceskip int, next bool) {
 	if trace.enabled {
 		traceGoUnpark(gp, traceskip)
 	}
@@ -550,7 +550,7 @@ func ready(gp *g, traceskip int) {
 
 	// status is Gwaiting or Gscanwaiting, make Grunnable and put on runq
 	casgstatus(gp, _Gwaiting, _Grunnable)
-	runqput(_g_.m.p.ptr(), gp, true)
+	runqput(_g_.m.p.ptr(), gp, next)
 	if atomic.Load(&sched.npidle) != 0 && atomic.Load(&sched.nmspinning) == 0 { // TODO: fast atomic
 		wakep()
 	}
@@ -1835,7 +1835,7 @@ top:
 	}
 	if fingwait && fingwake {
 		if gp := wakefing(); gp != nil {
-			ready(gp, 0)
+			ready(gp, 0, true)
 		}
 	}