[rtems commit] timecounter: Merge FreeBSD change r288216

[Sebastian Huber]

Module:    rtems
Branch:    master
Commit:    f013c1476e3c1184aa18d7e33fd219e253db192f
Changeset: http://git.rtems.org/rtems/commit/?id=f013c1476e3c1184aa18d7e33fd219e253db192f

Author:    Konstantin Belousov <kib at FreeBSD.org>
Date:      Fri Sep 25 13:03:57 2015 +0000

timecounter: Merge FreeBSD change r288216

Use per-cpu values for base and last in tc_cpu_ticks(). The values are updated lockess, different CPUs write its own view of timecounter state. The critical section is done for safety, callers of tc_cpu_ticks() are supposed to already enter critical section, or to own a spinlock.

The change fixes sporadical reports of too high values reported for
the (W)CPU on platforms that do not provide cpu ticker and use
tc_cpu_ticks(), in particular, arm*.

Diagnosed and reviewed by:	jhb
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week

Update #3175.

---

 cpukit/score/src/kern_tc.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/cpukit/score/src/kern_tc.c b/cpukit/score/src/kern_tc.c
index e6e952f..1e8189a 100644
--- a/cpukit/score/src/kern_tc.c
+++ b/cpukit/score/src/kern_tc.c
@@ -2183,20 +2183,27 @@ SYSINIT(timecounter, SI_SUB_CLOCKS, SI_ORDER_SECOND, inittimecounter, NULL);
 static int cpu_tick_variable;
 static uint64_t	cpu_tick_frequency;
 
+static DPCPU_DEFINE(uint64_t, tc_cpu_ticks_base);
+static DPCPU_DEFINE(unsigned, tc_cpu_ticks_last);
+
 static uint64_t
 tc_cpu_ticks(void)
 {
-	static uint64_t base;
-	static unsigned last;
-	unsigned u;
 	struct timecounter *tc;
+	uint64_t res, *base;
+	unsigned u, *last;
 
+	critical_enter();
+	base = DPCPU_PTR(tc_cpu_ticks_base);
+	last = DPCPU_PTR(tc_cpu_ticks_last);
 	tc = timehands->th_counter;
 	u = tc->tc_get_timecount(tc) & tc->tc_counter_mask;
-	if (u < last)
-		base += (uint64_t)tc->tc_counter_mask + 1;
-	last = u;
-	return (u + base);
+	if (u < *last)
+		*base += (uint64_t)tc->tc_counter_mask + 1;
+	*last = u;
+	res = u + *base;
+	critical_exit();
+	return (res);
 }
 
 void