[dpdk-dev] [PATCH] rte_alarm: modify it to make it not to be affected by discontinuous jumps in the system time

[Wen-Chi Yang]

Due to eal_alarm_callback() and rte_eal_alarm_set() use gettimeofday()
to get the current time, and gettimeofday() is affected by jumps.

For example, set up a rte_alarm which will be triggerd next second (
current time + 1 second) by rte_eal_alarm_set(). And the callback
function of this rte_alarm sets up another rte_alarm which will be
triggered next second (current time + 2 second).
Once we change the system time when the callback function is triggered,
it is possiblb that rte alarm functionalities work out of expectation.

Replace gettimeofday() with clock_gettime(CLOCK_MONOTONIC_RAW, &now)
could avoid this phenomenon.

Signed-off-by: Wen-Chi Yang <wolkayang at gmail.com>
---
 lib/librte_eal/linuxapp/eal/eal_alarm.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/lib/librte_eal/linuxapp/eal/eal_alarm.c 
b/lib/librte_eal/linuxapp/eal/eal_alarm.c
index a0eae1e..ff57323 100644
--- a/lib/librte_eal/linuxapp/eal/eal_alarm.c
+++ b/lib/librte_eal/linuxapp/eal/eal_alarm.c
@@ -99,14 +99,14 @@ static void
 eal_alarm_callback(struct rte_intr_handle *hdl __rte_unused,
                void *arg __rte_unused)
 {
-       struct timeval now;
+       struct timespec now;
        struct alarm_entry *ap;

        rte_spinlock_lock(&alarm_list_lk);
        while ((ap = LIST_FIRST(&alarm_list)) !=NULL &&
-                       gettimeofday(&now, NULL) == 0 &&
+                       clock_gettime(CLOCK_MONOTONIC_RAW, &now) == 0 &&
                        (ap->time.tv_sec < now.tv_sec || (ap->time.tv_sec == 
now.tv_sec &&
-                                               ap->time.tv_usec <= 
now.tv_usec))){
+                                               (ap->time.tv_usec * NS_PER_US) 
<= now.tv_nsec))) {
                ap->executing = 1;
                ap->executing_id = pthread_self();
                rte_spinlock_unlock(&alarm_list_lk);
@@ -126,11 +126,11 @@ eal_alarm_callback(struct rte_intr_handle *hdl 
__rte_unused,
                atime.it_value.tv_sec = ap->time.tv_sec;
                atime.it_value.tv_nsec = ap->time.tv_usec * NS_PER_US;
                /* perform borrow for subtraction if necessary */
-               if (now.tv_usec > ap->time.tv_usec)
+               if (now.tv_nsec > (ap->time.tv_usec * NS_PER_US))
                        atime.it_value.tv_sec--, atime.it_value.tv_nsec += 
US_PER_S * NS_PER_US;

                atime.it_value.tv_sec -= now.tv_sec;
-               atime.it_value.tv_nsec -= now.tv_usec * NS_PER_US;
+               atime.it_value.tv_nsec -= now.tv_nsec;
                timerfd_settime(intr_handle.fd, 0, &atime, NULL);
        }
        rte_spinlock_unlock(&alarm_list_lk);
@@ -139,7 +139,7 @@ eal_alarm_callback(struct rte_intr_handle *hdl __rte_unused,
 int
 rte_eal_alarm_set(uint64_t us, rte_eal_alarm_callback cb_fn, void *cb_arg)
 {
-       struct timeval now;
+       struct timespec now;
        int ret = 0;
        struct alarm_entry *ap, *new_alarm;

@@ -152,12 +152,12 @@ rte_eal_alarm_set(uint64_t us, rte_eal_alarm_callback 
cb_fn, void *cb_arg)
                return -ENOMEM;

        /* use current time to calculate absolute time of alarm */
-       gettimeofday(&now, NULL);
+       clock_gettime(CLOCK_MONOTONIC_RAW, &now);

        new_alarm->cb_fn = cb_fn;
        new_alarm->cb_arg = cb_arg;
-       new_alarm->time.tv_usec = (now.tv_usec + us) % US_PER_S;
-       new_alarm->time.tv_sec = now.tv_sec + ((now.tv_usec + us) / US_PER_S);
+       new_alarm->time.tv_usec = ((now.tv_nsec / NS_PER_US) + us) % US_PER_S;
+       new_alarm->time.tv_sec = now.tv_sec + (((now.tv_nsec / NS_PER_US) + us) 
/ US_PER_S);

        rte_spinlock_lock(&alarm_list_lk);
        if (!handler_registered) {
-- 
1.9.1