* [Xenomai-help] system locks when calling Linux clock_gettime
@ 2012-03-13 18:06 Herrera-Bendezu, Luis
2012-03-13 18:22 ` Gilles Chanteperdrix
0 siblings, 1 reply; 3+ messages in thread
From: Herrera-Bendezu, Luis @ 2012-03-13 18:06 UTC (permalink / raw)
To: xenomai
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Hello,
Xenomai version 2.4.10, Linux version 2.6.30.3, CPU PPC.
I am trying to work around an issue where the Linux and Xenomai realtime clocks
drifts when Linux clock is updated by NTP. It was suggested in the mail exchange:
http://www.mail-archive.com/xenomai@xenomai.org
to use clock_gettime()/clock_settime() to keep both clocks in sync.
However, calling linux clock_gettime() from a Xenomai thread is causing system to
freeze after a few minutes as shown in the following test program where the interval
to re-sync clocks is small, 50 msec, to force error faster:
#include <pthread.h>
#include <time.h>
#include <rtdk.h>
#include <sys/mman.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
int __real_clock_gettime(clockid_t clock_id,
struct timespec *tp);
// Interval to sync clocks, 50 msec.
#define CLOCK_SYNC_NSEC_INTERVAL 50000000
// Maximum clock drift tolerated, 2 msec.
#define MAX_NSEC_DRIFT 2000000
void
make_rt_thread()
{
int retval = 0;
struct sched_param sparam;
sparam.sched_priority = 1;
if ((retval = pthread_setschedparam(pthread_self(),
SCHED_FIFO, &sparam)) != 0) {
rt_printf("pthread_setschedparam: %s\n", strerror(retval));
exit(retval);
}
}
// Get Xenomai and Linux realtime clocks.
//
// return 0 on success and -1 otherwise.
int
get_realtime_clocks(struct timespec *pxeno,
struct timespec *pposix)
{
if (clock_gettime(CLOCK_REALTIME, pxeno) != 0) {
rt_printf("%s: error clock_gettime\n", __FUNCTION__);
return -1;
}
if (__real_clock_gettime(CLOCK_REALTIME, pposix) != 0) {
rt_printf("%s: error __real_clock_gettime\n", __FUNCTION__);
return -1;
}
return 0;
}
// Synchronize Xenomai clock to Linux's.
int
sync_xeno_clock(struct timespec *pposix)
{
int retval;
retval = clock_settime(CLOCK_REALTIME, pposix);
if (retval != 0) {
return -1;
}
return 0;
}
int
main (int argc, char** argv)
{
struct timespec xeno_real, posix_real;
struct timespec sync_interval;
int retval;
mlockall(MCL_CURRENT | MCL_FUTURE);
make_rt_thread();
rt_print_auto_init(1);
rt_print_init(16384, "SYNC_RT");
// sync clocks.
retval = get_realtime_clocks(&xeno_real, &posix_real);
if (retval != 0) {
rt_printf("%s: cannot read clocks\n", __FUNCTION__);
exit(1);
}
retval = sync_xeno_clock(&posix_real);
if (retval != 0) {
rt_printf("%s: cannot sync clock\n", __FUNCTION__);
exit(1);
}
sync_interval.tv_sec = 0;
sync_interval.tv_nsec = CLOCK_SYNC_NSEC_INTERVAL;
// loop to keep clocks in sync.
while (1) {
nanosleep(&sync_interval, NULL);
retval = get_realtime_clocks(&xeno_real, &posix_real);
if (retval != 0) {
continue;
}
if (xeno_real.tv_sec != posix_real.tv_sec) {
// clocks drift, resync.
retval = sync_xeno_clock(&posix_real);
if (retval != 0) {
rt_printf("%s: cannot resync clock\n", __FUNCTION__);
continue;
}
} else if (labs(xeno_real.tv_nsec - posix_real.tv_nsec) >
MAX_NSEC_DRIFT) {
// clocks drift, resync.
retval = sync_xeno_clock(&posix_real);
if (retval != 0) {
rt_printf("%s: cannot resync clock\n", __FUNCTION__);
continue;
}
}
}
exit(1);
}
Thanks,
Luis
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Xenomai-help] system locks when calling Linux clock_gettime
2012-03-13 18:06 [Xenomai-help] system locks when calling Linux clock_gettime Herrera-Bendezu, Luis
@ 2012-03-13 18:22 ` Gilles Chanteperdrix
2012-03-13 18:35 ` Herrera-Bendezu, Luis
0 siblings, 1 reply; 3+ messages in thread
From: Gilles Chanteperdrix @ 2012-03-13 18:22 UTC (permalink / raw)
To: Herrera-Bendezu, Luis; +Cc: xenomai
On 03/13/2012 07:06 PM, Herrera-Bendezu, Luis wrote:
> Hello,
>
> Xenomai version 2.4.10, Linux version 2.6.30.3, CPU PPC.
>
> I am trying to work around an issue where the Linux and Xenomai realtime clocks
> drifts when Linux clock is updated by NTP. It was suggested in the mail exchange:
> http://www.mail-archive.com/xenomai@xenomai.org
>
> to use clock_gettime()/clock_settime() to keep both clocks in sync.
>
> However, calling linux clock_gettime() from a Xenomai thread is causing system to
> freeze after a few minutes as shown in the following test program where the interval
> to re-sync clocks is small, 50 msec, to force error faster:
Yes, this is a known issue too. You can only call __real_clock_gettime
when in secondary mode. So, preferably from a thread created with
__real_pthread_create.
Any chance of updating xenomai? Xenomai 2.6 allows accessing a clock
synchronized with Linux clock from xenomai threads, without even
emitting a system call depending on the architecture.
--
Gilles.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Xenomai-help] system locks when calling Linux clock_gettime
2012-03-13 18:22 ` Gilles Chanteperdrix
@ 2012-03-13 18:35 ` Herrera-Bendezu, Luis
0 siblings, 0 replies; 3+ messages in thread
From: Herrera-Bendezu, Luis @ 2012-03-13 18:35 UTC (permalink / raw)
To: xenomai
>On 03/13/2012 07:06 PM, Herrera-Bendezu, Luis wrote:
>> Hello,
>>
>> Xenomai version 2.4.10, Linux version 2.6.30.3, CPU PPC.
>>
>> I am trying to work around an issue where the Linux and Xenomai realtime clocks
>> drifts when Linux clock is updated by NTP. It was suggested in the mail exchange:
>> http://www.mail-archive.com/xenomai-core@gna.org/msg07646.html
>>
>> to use clock_gettime()/clock_settime() to keep both clocks in sync.
>>
>> However, calling linux clock_gettime() from a Xenomai thread is causing system to
>> freeze after a few minutes as shown in the following test program where the interval
>> to re-sync clocks is small, 50 msec, to force error faster:
>
> Yes, this is a known issue too. You can only call __real_clock_gettime
> when in secondary mode. So, preferably from a thread created with
> __real_pthread_create.
>
> Any chance of updating xenomai? Xenomai 2.6 allows accessing a clock
> synchronized with Linux clock from xenomai threads, without even
> emitting a system call depending on the architecture.
>
> --
> Gilles.
Updating to 2.6 is not possible at this time. Did notice that
CLOCK_HOST_REALTIME is available. One more reason to update.
Thanks,
Luis
^ permalink raw reply [flat|nested] 3+ messages in thread
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2012-03-13 18:06 [Xenomai-help] system locks when calling Linux clock_gettime Herrera-Bendezu, Luis
2012-03-13 18:22 ` Gilles Chanteperdrix
2012-03-13 18:35 ` Herrera-Bendezu, Luis
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