void
evcnt_inc(uint32_t c[2])
{
	int s;

	s = splhigh();
	if (++c[0] == 0) {
		membar_producer();
		c[1]++;
	}
	splx(s);
}

uint64_t
evcnt_read(uint32_t c[2])
{
	struct lwp *l = curlwp;
	uint64_t ncsw;
	uint32_t hi, lo;

again:
	ncsw = l->l_ncsw;
	__insn_barrier();
	hi = c[1];
	membar_consumer();
	lo = c[0];
	membar_consumer();
	__insn_barrier();
	if (hi != c[1] || ncsw != l->l_ncsw)
		goto again;

	return ((uint64_t)hi << 32) | lo;
}