Re: guest gettimeofday behavior

[Marcelo Tosatti <mtosatti@redhat.com>]

On Tue, Jul 07, 2009 at 09:58:46AM +0000, Eran Rom wrote:
> Eran Rom <eranr <at> il.ibm.com> writes:
> 
> > 
> > Eran Rom <eranr <at> il.ibm.com> writes:
> > 
> > Still getting a misbehaving clock:
> > guest uses kvmclock with kernel 2.6.27
> > host kernel is 2.6.27 with kvm-qemu-87 & kvm-kmod-87
> > 
> > getting:
> > ...
> > now     =       2128043797
> > now     =       2138048010
> > now     =       18446744071562636328
> > 

Eran,

This was happening with kvmclock back then when it did not handle
cpu frequency changes. What are the details of the host hw?

Glauber, any clues?

> Below is the exact code used.
> Also, I use a script in the host to run this code in a loop for 5 minutes, each
> time in a newly launched guest. This happens on average once every 10 executions.
> 
> Thanks very much,
> Eran
> 
> #include <sys/time.h>
> #include <time.h>
> 
> int main(int argc, char **argv)
> {
>         int seconds;
>         unsigned long long now, goal;
>         struct timeval time1, time2;
> 
>         if (argc != 2)
>                 return;
> 
>         seconds = atoi(argv[1]);
> 
>         gettimeofday(&time1, NULL);
>         now = ((time1.tv_sec) * 1000000) + time1.tv_usec;
>         goal = now + (seconds * 1000000);
>         while (now < goal) {
>                 sleep(10);
>                 gettimeofday(&time2, NULL);
>                 now = (time2.tv_sec * 1000000) + time2.tv_usec;
>         }
> }