if !pp.trace.acquireStatus(w.gen) {
		return w
	}
	var status traceProcStatus
	switch pp.status {
	case _Pidle, _Pgcstop:
		status = traceProcIdle
		if pp.status == _Pgcstop && inSTW {
			// N.B. a P that is running and currently has the world stopped will be
			// in _Pgcstop, but we model it as running in the tracer.
			status = traceProcRunning
		}
	case _Prunning:
		status = traceProcRunning

	// after a syscall, it must understand the P may have been
	// used by another M in the interim.
	_Psyscall

	// _Pgcstop means a P is halted for STW and owned by the M
	// that stopped the world. The M that stopped the world
	// continues to use its P, even in _Pgcstop. Transitioning
	// from _Prunning to _Pgcstop causes an M to release its P and
	// park.
	//
	// The P retains its run queue and startTheWorld will restart

	// serialized by the caller.
	trace.seqGC++
}

// STWStart traces a STWBegin event.
func (tl traceLocker) STWStart(reason stwReason) {
	// Although the current P may be in _Pgcstop here, we model the P as running during the STW. This deviates from the
	// runtime's state tracking, but it's more accurate and doesn't result in any loss of information.

	preemptall()
	// stop current P
	gp.m.p.ptr().status = _Pgcstop // Pgcstop is only diagnostic.
	gp.m.p.ptr().gcStopTime = start
	sched.stopwait--
	// try to retake all P's in Psyscall status
	trace = traceAcquire()
	for _, pp := range allp {
		s := pp.status
		if s == _Psyscall && atomic.Cas(&pp.status, s, _Pgcstop) {
			if trace.ok() {
				trace.ProcSteal(pp, false)
			}

	s.IdleTime += sched.idleTime.Load()

	// Compute userTime. We compute this indirectly as everything that's not the above.
	//
	// Since time spent in _Pgcstop is covered by gcPauseTime, and time spent in _Pidle
	// is covered by idleTime, what we're left with is time spent in _Prunning and _Psyscall,
	// the latter of which is fine because the P will either go idle or get used for something