if gp.preempt {
					// We were preempted. This is
					// a useful signal to kick
					// everything out of the run
					// queue so it can run
					// somewhere else.
					if drainQ, n := runqdrain(pp); n > 0 {
						lock(&sched.lock)
						globrunqputbatch(&drainQ, int32(n))
						unlock(&sched.lock)
					}
				}
				// Go back to draining, this time
				// without preemption.

		if atomic.CasRel(&pp.runqhead, h, h+1) { // cas-release, commits consume
			return gp, false
		}
	}
}

// runqdrain drains the local runnable queue of pp and returns all goroutines in it.
// Executed only by the owner P.
func runqdrain(pp *p) (drainQ gQueue, n uint32) {
	oldNext := pp.runnext
	if oldNext != 0 && pp.runnext.cas(oldNext, 0) {
		drainQ.pushBack(oldNext.ptr())
		n++
	}