If the clock interrupt advances for more than one tick, we obviously
lost a number of clock ticks. That might happen in a virtual machine
that does not get scheduled in time. There is no point in creating a
cluster of events with basically the same timestamp and identical stack
traces. Generate only one event instead and drop all skipped ticks.

 - Christian

---
 sys/dev/dt/dt_dev.c          | 12 ++++++++++--
 sys/dev/dt/dt_prov_profile.c | 17 ++++++++++-------
 sys/dev/dt/dtvar.h           |  1 +
 3 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/sys/dev/dt/dt_dev.c b/sys/dev/dt/dt_dev.c
index 75fbbba6a575..286bda80992d 100644
--- a/sys/dev/dt/dt_dev.c
+++ b/sys/dev/dt/dt_dev.c
@@ -725,6 +725,15 @@ dt_pcb_purge(struct dt_pcb_list *plist)
 	}
 }
 
+void
+dt_pcb_ring_drop(struct dt_pcb *dp, unsigned int drop)
+{
+	struct dt_cpubuf *dc = &dp->dp_sc->ds_cpu[cpu_number()];
+
+	dc->dc_dropevt += drop;
+	membar_producer();
+}
+
 /*
  * Get a reference to the next free event state from the ring.
  */
@@ -747,8 +756,7 @@ dt_pcb_ring_get(struct dt_pcb *dp, int profiling)
 	distance = prod - cons;
 	if (distance == 1 || distance == (1 - DT_EVTRING_SIZE)) {
 		/* read(2) isn't finished */
-		dc->dc_dropevt++;
-		membar_producer();
+		dt_pcb_ring_drop(dp, 1);
 
 		dc->dc_inevt = 0;
 		return NULL;
diff --git a/sys/dev/dt/dt_prov_profile.c b/sys/dev/dt/dt_prov_profile.c
index 62900152e147..5e4d9f1a2081 100644
--- a/sys/dev/dt/dt_prov_profile.c
+++ b/sys/dev/dt/dt_prov_profile.c
@@ -101,15 +101,18 @@ dt_prov_profile_alloc(struct dt_probe *dtp, struct dt_softc *sc,
 void
 dt_clock(struct clockrequest *cr, void *cf, void *arg)
 {
-	uint64_t count, i;
+	uint64_t count;
 	struct dt_evt *dtev;
 	struct dt_pcb *dp = arg;
 
 	count = clockrequest_advance(cr, dp->dp_nsecs);
-	for (i = 0; i < count; i++) {
-		dtev = dt_pcb_ring_get(dp, 1);
-		if (dtev == NULL)
-			return;
-		dt_pcb_ring_consume(dp, dtev);
-	}
+	if (count == 0)
+		return;
+	else if (count > 1)
+		dt_pcb_ring_drop(dp, count - 1);
+
+	dtev = dt_pcb_ring_get(dp, 1);
+	if (dtev == NULL)
+		return;
+	dt_pcb_ring_consume(dp, dtev);
 }
diff --git a/sys/dev/dt/dtvar.h b/sys/dev/dt/dtvar.h
index c6cfa7f66b3b..a1f6037e3233 100644
--- a/sys/dev/dt/dtvar.h
+++ b/sys/dev/dt/dtvar.h
@@ -179,6 +179,7 @@ struct dt_pcb	*dt_pcb_alloc(struct dt_probe *, struct dt_softc *);
 void		 dt_pcb_free(struct dt_pcb *);
 void		 dt_pcb_purge(struct dt_pcb_list *);
 
+void		 dt_pcb_ring_drop(struct dt_pcb *, unsigned int);
 struct dt_evt	*dt_pcb_ring_get(struct dt_pcb *, int);
 void		 dt_pcb_ring_consume(struct dt_pcb *, struct dt_evt *);
 
-- 
2.34.1

• smime.p7s (5K)