Function cpu_lock_delay

freebsd/x86/x86/delay.c:126–143

}

void
cpu_lock_delay(void)
{

	/*
	 * Use TSC to wait for a usec if present, otherwise fall back
	 * to reading from port 0x84.  We can't call into timecounters
	 * for this delay since timecounters might use spin locks.
	 *
	 * Note that unlike delay_tc(), this uses the TSC even if it
	 * is not P-state invariant.  For this function it is ok to
	 * wait even a few usecs.
	 */
	if (tsc_freq != 0)
		delay_tsc(1);
	else
		inb(0x84);
}