Re: [timer/ticks related] dom0 hang during boot on large 1TB system

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 12/21/2009 02:47 PM, Mukesh Rathor wrote:
> delta comes from:
>
> timer_inetrrupt() in time-xen.c :
> ...
>          do {
>                  get_time_values_from_xen(cpu);
>
>                  /* Obtain a consistent snapshot of elapsed wallclock cycles. */
>        --->       delta = delta_cpu =
>                          shadow->system_timestamp + get_nsec_offset(shadow);
>        --->       delta     -= processed_system_time;
>                  delta_cpu -= per_cpu(processed_system_time, cpu);
>
>                  /*
>                   * Obtain a consistent snapshot of stolen/blocked cycles. We
>                   * can use state_entry_time to detect if we get preempted here.
>                   */
>                  do {
>                          sched_time = runstate->state_entry_time;
>                          barrier();
>                          stolen = runstate->time[RUNSTATE_runnable] +
>                                  runstate->time[RUNSTATE_offline] -
>                                  per_cpu(processed_stolen_time, cpu);
>                          blocked = runstate->time[RUNSTATE_blocked] -
>                                  per_cpu(processed_blocked_time, cpu);
>                          barrier();
>                  } while (sched_time != runstate->state_entry_time);
>          } while (!time_values_up_to_date(cpu));
> ...
>
>
> At first glance, i don't understand the above algorithm. Since you've
> the same code, I assumed you could also compute delta to be a large
> value when dom0 starts, in which case you may observe dom0 hang.
>    

There's some code in the pvops kernel which looks vaguely like that, but 
it has nothing to do with timer interrupts.  Could you be more specific 
about what you're referring to?

     J