Re: [Xen-devel] Re: [PATCH] xen: always handle VIRQ_TIMER first.

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 17.10.10 at 08:11, Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:
> I think (but I haven't spelunked into that code lately) that after a
> tickless idle period it will update jiffies N ticks based on the
> clocksource, and then run any other interrupt handler code, so jiffies
> will always appear to be up to date.
> 
> Ah, yes, here it is:
> 
> /**
>  * tick_nohz_update_jiffies - update jiffies when idle was interrupted
>  *
>  * Called from interrupt entry when the CPU was idle
>  *
>  * In case the sched_tick was stopped on this CPU, we have to check if 
> jiffies
>  * must be updated. Otherwise an interrupt handler could use a stale jiffy
>  * value. We do this unconditionally on any cpu, as we don't know whether 
> the
>  * cpu, which has the update task assigned is in a long sleep.
>  */
> static void tick_nohz_update_jiffies(ktime_t now)
> {
>       ...
> }

But this is available only with CONFIG_NO_HZ, which is a freely
selectable option. So perhaps the code should still be added
inside an #ifndef CONFIG_NO_HZ?

Jan


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