[Xenomai-core] [RFC][PATCH 4/4] shorten overrun loops of periodic timers

[Jan Kiszka <jan.kiszka@domain.hid>]

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A simple patch, just like suggested by Gilles, to avoid looping over
periodic xntimer handlers in case of overruns.

It saves the current TSC on loop entry and uses this value later when
forwarding the timer. Is is the overhead of re-reading the TSC on all
archs negligible and should we rather go that way?

Jan

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---
 ksrc/nucleus/timer.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

Index: xenomai/ksrc/nucleus/timer.c
===================================================================
--- xenomai.orig/ksrc/nucleus/timer.c
+++ xenomai/ksrc/nucleus/timer.c
@@ -200,12 +200,13 @@ static void xntimer_do_tick_aperiodic(vo
 	xntimerq_t *timerq = &sched->timerqueue;
 	xntimerh_t *holder;
 	xntimer_t *timer;
+	xnticks_t now;
 
 	while ((holder = xntimerq_head(timerq)) != NULL) {
 		timer = aplink2timer(holder);
 
-		if (xntimerh_date(&timer->aplink) - nkschedlat >
-		    xnarch_get_cpu_tsc())
+		now = xnarch_get_cpu_tsc();
+		if (xntimerh_date(&timer->aplink) - nkschedlat > now)
 			/* No need to continue in aperiodic mode since timeout
 			   dates are ordered by increasing values. */
 			break;
@@ -236,8 +237,8 @@ static void xntimer_do_tick_aperiodic(vo
 				}
 #endif /* CONFIG_XENO_OPT_DEBUG || __XENO_SIM__ */
 			} else if (timer->interval == XN_INFINITE) {
-				xntimerh_date(&timer->aplink) +=
-				    nkpod->htimer.interval;
+				while ((xntimerh_date(&timer->aplink) +=
+				        nkpod->htimer.interval) < now);
 				continue;
 			}
 		} else

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