Time going backwards 2005-12-03 - By Ed Wilts
Back
I'm working with a 3rd party vendor whose software isn't happy with our
time going backwards. This is happening even without ntp running. It
isn't consistent on all systems, but I've got at least 2 DL380 dual-cpu
systems that have this issue. So far I've seen it only on these 2 DL380
systems (both happen to have fiber cards in them). Other DL380s running
the same release don't have the problem (but none have fiber cards -
whether that has any bearing on the problem or not I don't know). These
are all running fully up2date RHEL 3. All have hyperthreading enabled
on 3.06 Ghz Xeon processors.
Can anybody shed any light on just where to look? I'm attaching a very
short C program that demonstrates the time shifts. On my of my servers,
after 914 passes through (about 6 minutes), the time jumped backwards 14
times.
Any ideas would be GREATLY appreciated.
Thanks,
.../Ed
[ewilts@(protected) ewilts]$ cat as-timetest.c
#include <stdio.h>
#include <bits/time.h>
#include <sys/time.h>
int main(int argc, char *argv[])
{
struct timeval t, old, delta;
while (1) {
usleep(400000);
gettimeofday(&t, NULL);
printf("%ld %ld\n", t.tv_sec, t.tv_usec);
if (old.tv_sec > t.tv_sec) {
delta.tv_sec = t.tv_sec - old.tv_sec;
delta.tv_usec = t.tv_usec - old.tv_usec;
printf("Delta time: %ld %ld\n", delta.tv_sec, delta.tv_usec);
}
old = t;
}
return 0;
}
--
Ed Wilts, RHCE
Mounds View, MN, USA
mailto:ewilts@(protected)
Member #1, Red Hat Community Ambassador Program
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