Re: [Qemu-devel] [PATCH v8 2/4] hw/ptimer: Perform tick and counter wrap around if timer already expired

[Dmitry Osipenko <digetx@gmail.com>]

06.01.2016 16:59, Peter Crosthwaite пишет:

>>>> +
>>>> +            if (expired) {
>>>> +                /* Wrap around periodic counter.  */
>>>> +                counter = s->delta = s->limit - counter % s->limit;
>>>
>>>
>>> Why do you update the delta here?
>>>
>>
>> Because we would want to schedule next tick based on current wrapped around
>> counter value and not some arbitrary delta.
>>
>
> So looking at ptimer_reload(), the new schedule is done relative to
> the VM clock of the when the tick was expected to hit, not the current
> time. But this new delta is going to be relative to the now time and
> then used to update the next tick which will happen relative to
> next_event. Unless you stop or scale the timer, I don't think you need
> to do delta manipulation?
>

Yes, I missed that next_event would be set earlier (like you described) in case 
of expired timer. Thanks for the note, will fix it.

>>> Also can you just get ptimer_reload to do the modulo math for you? If the
>>> timer is !oneshot and expired, then you call ptimer_reload anyway,
>>> which will update next_event. When the expired test returns false
>>> you can just reliably use the original logic involving now and next.
>>>
>>
>> Yes, that's what I changed in V9. Have you received it?
>>
>> https://lists.nongnu.org/archive/html/qemu-devel/2016-01/msg00272.html
>>
>
> Just had a look.
>
> V9 still has the modulo I think?:
>
> +            if (expired && (counter != 0)) {
> +                /* Wrap around periodic counter.  */
> +                counter = s->delta = s->limit - counter % s->limit;
> +            }
>

Modulo is there, I just meant that V9 changed to call ptimer_reload() on counter 
== 0. As noted above, ptimer_reload would adjust next_event, so s->delta
shouldn't be set to the wrapped around counter. However it should be set to the 
limit, since delta might been altered by ptimer_set_count.

-- 
Dmitry