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xen-devel
RE: [Xen-devel] vpt periodic timer and vhpet
>From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
>Sent: Friday, February 06, 2009 4:24 PM
>
>On 06/02/2009 03:55, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
>
>> Just noted vpt create_periodic_time is now changed to require
>> two parameters: period and delta, by 18694 which ports vhpet
>> to vpt framework. I'm not quite clear the necessity here. It doesn't
>> matter whether 1st expiration must be accurately hit. vhpet
>> main counter and per-channel comparators are updated only
>> when guest tries to read. Is there any special tricks on hpet
>> since all other periodic timers are simply filling same value for
>> period and delta?
>>
>> I ask because we're considering some proactive timer alignment
>> besides existing range timer, while above change seems to implicate
>> something that we may neglect.
>
>See the changeset that introduced the delta (18694), see the changeset
>comment and the comment above use of create_periodic_time() in hpet.c.
>Decide if you agree, and if you don't then ask the author,
>cc'ing the list.
>
I read those comments, and agree that 1st expected expiration from now
could be different from period, but I don't see the necessity to emulate
this difference for a periodic timer, since later expirations could be also
inaccurate which is handled by vpt logic. Then why 1st trigger needs special
care?
CC peter now.
Thanks,
Kevin
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