Notes:

1.
======================================================================
When ACPI is turned on, interrupt storm is detected on em during
boot and machine simply stops. I don't know whether the problem
is caused by the bug in BIOS or in em driver. Turning ACPI off
in BIOS and em works fine.
======================================================================

2.
======================================================================
Without applying attached patch against sys/i386/isa/clock.c,
systat, top and vmstat don't show CPU usage under 5.3-BETA4 and
5.3-STABLE as of 6th Jan. 2005. System, user and idle are always 0%.
Search PR 17800 for original problem report.
======================================================================





============== Here's the patch: =====================================


--- sys/i386/isa/clock.c.orig	Mon Jul 12 02:50:59 2004
+++ sys/i386/isa/clock.c	Thu Jan  6 21:13:48 2005
@@ -946,6 +946,7 @@
 	/* Initialize RTC. */
 	writertc(RTC_STATUSA, rtc_statusa);
 	writertc(RTC_STATUSB, RTCSB_24HR);
+	rtcin(RTC_INTR); /* clear any pending interrupt */
 
 	/* Don't bother enabling the statistics clock. */
 	if (!statclock_disable) {