--- include/clock.h@@/main/sandvine_plt_neutron/0	2007-10-05 14:32:29.000000000 -0400
+++ include/clock.h@@/main/sandvine_plt_neutron/1	2007-10-09 11:14:15.000000000 -0400
@@ -38,6 +38,7 @@ int	sysbeep(int pitch, int period);
 void	timer_restore(void);
 void	init_TSC(void);
 void	init_TSC_tc(void);
+void	DELAY_TSCCAL(int n);
 
 #endif /* _KERNEL */
 
--- isa/clock.c@@/main/RELENG_6/sandvine_bsd_6_main/sandvine_plt_neutron/1	2007-03-09 17:24:23.000000000 -0500
+++ isa/clock.c@@/main/RELENG_6/sandvine_bsd_6_main/sandvine_plt_neutron/2	2007-10-09 11:15:01.000000000 -0400
@@ -142,7 +142,7 @@ static	u_char	timer2_state;
 
 static	unsigned i8254_get_timecount(struct timecounter *tc);
 static	unsigned i8254_simple_get_timecount(struct timecounter *tc);
-static	void	set_timer_freq(u_int freq, int intr_freq);
+static	void	set_timer_freq(u_int freq, int intr_freq, int freerun);
 
 static struct timecounter i8254_timecounter = {
 	i8254_get_timecount,	/* get_timecount */
@@ -308,7 +308,7 @@ DELAY(int n)
 	 * early for console i/o.
 	 */
 	if (timer0_max_count == 0)
-		set_timer_freq(timer_freq, hz);
+		set_timer_freq(timer_freq, hz, 0);
 
 	/*
 	 * Read the counter first, so that the rest of the setup overhead is
@@ -388,6 +388,20 @@ DELAY(int n)
 #endif
 }
 
+/*
+ * XXX This is a gross hack for reqst00084792.  The tsc clock frequency was
+ * being miscalibrated by about 0.1%, due to some issue with a new BIOS version
+ * from SuperMicro.  To avoid the issue we let the i8254 counter free run so
+ * that we're virtually guaranteed not to miss a counter rollover.
+ */
+void
+DELAY_TSCCAL(int n)
+{
+	set_timer_freq(timer_freq, hz, 1);
+	DELAY(n);
+	set_timer_freq(timer_freq, hz, 0);
+}
+
 static void
 sysbeepstop(void *chan)
 {
@@ -535,18 +549,19 @@ fail:
 	if (bootverbose)
 	        printf("failed, using default i8254 clock of %u Hz\n",
 		       timer_freq);
+
 	return (timer_freq);
 }
 
 static void
-set_timer_freq(u_int freq, int intr_freq)
+set_timer_freq(u_int freq, int intr_freq, int freerun)
 {
 	int new_timer0_real_max_count;
 
 	i8254_timecounter.tc_frequency = freq;
 	mtx_lock_spin(&clock_lock);
 	timer_freq = freq;
-	if (using_lapic_timer)
+	if (using_lapic_timer || freerun)
 		new_timer0_real_max_count = 0x10000;
 	else
 		new_timer0_real_max_count = TIMER_DIV(intr_freq);
@@ -613,7 +628,7 @@ startrtclock()
 	writertc(RTC_STATUSA, rtc_statusa);
 	writertc(RTC_STATUSB, RTCSB_24HR);
 
-	set_timer_freq(timer_freq, hz);
+	set_timer_freq(timer_freq, hz, 0);
 	freq = calibrate_clocks();
 #ifdef CLK_CALIBRATION_LOOP
 	if (bootverbose) {
@@ -645,7 +660,7 @@ startrtclock()
 			       freq, timer_freq);
 	}
 
-	set_timer_freq(timer_freq, hz);
+	set_timer_freq(timer_freq, hz, 0);
 	tc_init(&i8254_timecounter);
 
 	init_TSC();
@@ -815,7 +830,7 @@ cpu_initclocks()
 		i8254_timecounter.tc_get_timecount =
 		    i8254_simple_get_timecount;
 		i8254_timecounter.tc_counter_mask = 0xffff;
-		set_timer_freq(timer_freq, hz);
+		set_timer_freq(timer_freq, hz, 0);
 	}
 
 	/* Initialize RTC. */
@@ -884,7 +899,7 @@ sysctl_machdep_i8254_freq(SYSCTL_HANDLER
 	freq = timer_freq;
 	error = sysctl_handle_int(oidp, &freq, sizeof(freq), req);
 	if (error == 0 && req->newptr != NULL)
-		set_timer_freq(freq, hz);
+		set_timer_freq(freq, hz, 0);
 	return (error);
 }
 
--- i386/tsc.c@@/main/sandvine_plt_neutron/0	2007-09-21 10:29:02.000000000 -0400
+++ i386/tsc.c@@/main/sandvine_plt_neutron/1	2007-10-09 11:15:30.000000000 -0400
@@ -80,7 +80,7 @@ init_TSC(void)
 	        printf("Calibrating TSC clock ... ");
 
 	tscval[0] = rdtsc();
-	DELAY(1000000);
+	DELAY_TSCCAL(1000000);
 	tscval[1] = rdtsc();
 
 	tsc_freq = tscval[1] - tscval[0];