[rtems commit] Make timehands count selectable at boottime.

[Jan Sommer]

Module:    rtems
Branch:    5
Commit:    402dafa4954d33fe177fc5e5b789abbf407909ca
Changeset: http://git.rtems.org/rtems/commit/?id=402dafa4954d33fe177fc5e5b789abbf407909ca

Author:    Konstantin Belousov <kib at FreeBSD.org>
Date:      Mon Sep  9 11:29:58 2019 +0000

Make timehands count selectable at boottime.

Tested by:	O'Connor, Daniel <darius at dons.net.au>
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D21563

This patch was modified by Sebastian Huber
<sebastian.huber at embedded-brains.de> to adjust it for RTEMS.  See
comment in the patch.

---

 cpukit/score/src/kern_tc.c | 50 +++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 45 insertions(+), 5 deletions(-)

diff --git a/cpukit/score/src/kern_tc.c b/cpukit/score/src/kern_tc.c
index 21d018a..3aa68f7 100644
--- a/cpukit/score/src/kern_tc.c
+++ b/cpukit/score/src/kern_tc.c
@@ -167,6 +167,35 @@ struct timehands {
 	struct timehands	*th_next;
 };
 
+#ifndef __rtems__
+static struct timehands ths[16] = {
+    [0] =  {
+	.th_counter = &dummy_timecounter,
+	.th_scale = (uint64_t)-1 / 1000000,
+	.th_offset = { .sec = 1 },
+	.th_generation = 1,
+    },
+};
+
+static struct timehands *volatile timehands = &ths[0];
+struct timecounter *timecounter = &dummy_timecounter;
+static struct timecounter *timecounters = &dummy_timecounter;
+
+int tc_min_ticktock_freq = 1;
+#else /* __rtems__ */
+/*
+ * In FreeBSD, the timehands count is a tuning option from two to 16.  The
+ * tuning option was added since it is inexpensive and some FreeBSD users asked
+ * for it to play around.  The default value is two.  One system which did not
+ * work with two timehands was a system with one processor and a specific PPS
+ * device.
+ *
+ * For RTEMS, in uniprocessor configurations, just use one timehand since the
+ * update is done with interrupt disabled.
+ *
+ * In SMP configurations, use a fixed set of two timehands until someone
+ * reports an issue.
+ */
 #if defined(RTEMS_SMP)
 static struct timehands th0;
 static struct timehands th1 = {
@@ -193,10 +222,6 @@ static struct timehands th0 = {
 
 static struct timehands *volatile timehands = &th0;
 struct timecounter *timecounter = &dummy_timecounter;
-#ifndef __rtems__
-static struct timecounter *timecounters = &dummy_timecounter;
-
-int tc_min_ticktock_freq = 1;
 #endif /* __rtems__ */
 
 #ifndef __rtems__
@@ -219,6 +244,10 @@ static int timestepwarnings;
 SYSCTL_INT(_kern_timecounter, OID_AUTO, stepwarnings, CTLFLAG_RW,
     &timestepwarnings, 0, "Log time steps");
 
+static int timehands_count = 2;
+SYSCTL_INT(_kern_timecounter, OID_AUTO, timehands_count, CTLFLAG_RDTUN,
+    &timehands_count, 0, "Count of timehands in rotation");
+
 struct bintime bt_timethreshold;
 struct bintime bt_tickthreshold;
 sbintime_t sbt_timethreshold;
@@ -2216,8 +2245,9 @@ done:
 static void
 inittimecounter(void *dummy)
 {
+	struct timehands *thp;
 	u_int p;
-	int tick_rate;
+	int i, tick_rate;
 
 	/*
 	 * Set the initial timeout to
@@ -2243,6 +2273,16 @@ inittimecounter(void *dummy)
 #ifdef FFCLOCK
 	ffclock_init();
 #endif
+
+	/* Set up the requested number of timehands. */
+	if (timehands_count < 1)
+		timehands_count = 1;
+	if (timehands_count > nitems(ths))
+		timehands_count = nitems(ths);
+	for (i = 1, thp = &ths[0]; i < timehands_count;  thp = &ths[i++])
+		thp->th_next = &ths[i];
+	thp->th_next = &ths[0];
+
 	/* warm up new timecounter (again) and get rolling. */
 	(void)timecounter->tc_get_timecount(timecounter);
 	(void)timecounter->tc_get_timecount(timecounter);