Re: [Xen-devel] late lapic timer interrupts for hvm guest

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 28/10/08 07:45, "Juergen Gross" <juergen.gross@xxxxxxxxxxxxxxxxxxx>
wrote:

>      pt->scheduled = NOW() + period;
>      /*
>       * Offset LAPIC ticks from other timer ticks. Otherwise guests which use
>       * LAPIC ticks for process accounting can see long sequences of process
>       * ticks incorrectly accounted to interrupt processing.
>       */
>      if ( pt->source == PTSRC_lapic )
>          pt->scheduled += period >> 1;
> 
> We have ported our mainframe OS BS2000 to x86_64/XEN and we are using the
> lapic timer as the main timer interrupt source (one shot mode). Finally I've
> found the above coding which seems to be the root cause of late interrupts.
> 
> I think the problem mentioned in the comment won't occur if the guest uses
> the lapic timer in one shot mode with varying timer values (like BS2000). Or
> am I wrong here?

Right. That extra code could be conditional on setting up a periodic LAPIC
timer.

 -- Keir



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