This along with v1.6 of counter.c fixes some timecounter issues on

MP machines (hopefully).  CPU timers are OK on UP machines but we
don't keep the timers in sync on MP machines so if the CPU's timer
is chosen as the primary timecounter it's possible for time to
not be monotonically increasing because different CPU's counters
may be used at different times.  But the CPU's counters are otherwise
one of the higher quality counters available.  So, on UP machines
we'll use a relatively high quality value but on MP machines we'll
use a quality that should prevent the CPU's counters from being chosen.

Requested by:	green (who did the first version of the patch)
Reviewed by:	marius, green
MFC after:	1 week

1 files changed, 19 insertions, 0 deletions

diff --git a/sys/sparc64/sparc64/machdep.c b/sys/sparc64/sparc64/machdep.c
index 582930d..f7f08c4 100644
--- a/sys/sparc64/sparc64/machdep.c
+++ b/sys/sparc64/sparc64/machdep.c
@@ -132,6 +132,16 @@ struct kva_md_info kmi;
 u_long ofw_vec;
 u_long ofw_tba;
 
+/*
+ * Note: timer quality for CPU's is set low to try and prevent them from
+ * being chosen as the primary timecounter.  The CPU counters are not
+ * synchronized among the CPU's so in MP machines this causes problems
+ * when calculating the time.  With this value the CPU's should only be
+ * chosen as the primary timecounter as a last resort.
+ */
+
+#define	UP_TICK_QUALITY	1000
+#define	MP_TICK_QUALITY	-100
 static struct timecounter tick_tc;
 
 char sparc64_model[32];
@@ -174,6 +184,15 @@ cpu_startup(void *arg)
 	tick_tc.tc_counter_mask = ~0u;
 	tick_tc.tc_frequency = tick_freq;
 	tick_tc.tc_name = "tick";
+	tick_tc.tc_quality = UP_TICK_QUALITY;
+#ifdef SMP
+	/*
+	 * We do not know if each CPU's tick counter is synchronized.
+	 */
+	if (cpu_mp_probe())
+		tick_tc.tc_quality = MP_TICK_QUALITY;
+#endif
+
 	tc_init(&tick_tc);
 
 	physsz = 0;