From 04257819a4d326980d051f445ae317d8cd16374b Mon Sep 17 00:00:00 2001
From: phk <phk@FreeBSD.org>
Date: Fri, 26 Apr 2002 12:37:36 +0000
Subject: Move the winding of timecounters out of hardclock and into a normal
 timeout loop.

Limit the rate at which we wind the timecounters to approx 1000 Hz.

This limits the precision of the get{bin,nano,micro}[up]time(9)
functions to roughly a millisecond.
---
 sys/kern/kern_clock.c |  3 ---
 sys/kern/kern_tc.c    | 40 +++++++++++++++++++++++++++++++++++++++-
 2 files changed, 39 insertions(+), 4 deletions(-)

(limited to 'sys/kern')

diff --git a/sys/kern/kern_clock.c b/sys/kern/kern_clock.c
index e613eb6..92175b8 100644
--- a/sys/kern/kern_clock.c
+++ b/sys/kern/kern_clock.c
@@ -53,8 +53,6 @@
 #include <sys/resourcevar.h>
 #include <sys/signalvar.h>
 #include <sys/smp.h>
-#include <sys/timetc.h>
-#include <sys/timepps.h>
 #include <vm/vm.h>
 #include <vm/pmap.h>
 #include <vm/vm_map.h>
@@ -218,7 +216,6 @@ hardclock(frame)
 	if (stathz == 0)
 		statclock(frame);
 
-	tc_windup();
 #ifdef DEVICE_POLLING
 	hardclock_device_poll();	/* this is very short and quick */
 #endif /* DEVICE_POLLING */
diff --git a/sys/kern/kern_tc.c b/sys/kern/kern_tc.c
index d403847..aee3eaa 100644
--- a/sys/kern/kern_tc.c
+++ b/sys/kern/kern_tc.c
@@ -50,6 +50,8 @@ TC_STATS(ngetbintime);   TC_STATS(ngetnanotime);   TC_STATS(ngetmicrotime);
 
 #undef TC_STATS
 
+static void tc_windup(void);
+
 /*
  * Implement a dummy timecounter which we can use until we get a real one
  * in the air.  This allows the console and other early stuff to use
@@ -332,7 +334,7 @@ switch_timecounter(struct timecounter *newtc)
 	splx(s);
 }
 
-void
+static void
 tc_windup(void)
 {
 	struct timecounter *tc, *tco;
@@ -547,3 +549,39 @@ pps_event(struct pps_state *pps, struct timecounter *tc, unsigned count, int eve
 	}
 #endif
 }
+
+/*-
+ * Timecounters need to be updated every so often to prevent the hardware
+ * counter from overflowing.  Updating also recalculates the cached values
+ * used by the get*() family of functions, so their precision depends on
+ * the update frequency.
+ * Don't update faster than approx once per millisecond, if people want
+ * better timestamps they should use the non-"get" functions.
+ */
+
+static int tc_tick;
+SYSCTL_INT(_kern_timecounter, OID_AUTO, tick, CTLFLAG_RD, &tick, 0, "");
+
+static void
+tc_ticktock(void *dummy)
+{
+
+	tc_windup();
+	timeout(tc_ticktock, NULL, tc_tick);
+}
+
+static void 
+inittimecounter(void *dummy)
+{
+	u_int p;
+
+	if (hz > 1000)
+		tc_tick = (hz + 500) / 1000;
+	else
+		tc_tick = 1;
+	p = (tc_tick * 1000000) / hz;
+	printf("Timecounters tick every %d.%03u msec\n", p / 1000, p % 1000);
+	tc_ticktock(NULL);
+}
+
+SYSINIT(timecounter, SI_SUB_CLOCKS, SI_ORDER_FIRST, inittimecounter, NULL)
-- 
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