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Re: [Xen-devel] Question about hpet calls to set_timer

  • To: Beth Kon <eak@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
  • Date: Sun, 17 Aug 2008 11:25:22 +0100
  • Cc:
  • Delivery-date: Sun, 17 Aug 2008 03:25:49 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AckAU43qzD9QlGxGEd24dgAWy6hiGQ==
  • Thread-topic: [Xen-devel] Question about hpet calls to set_timer

I might use 'hg anno' to see if anyone changed it to period for good reason,
but it seems to me that your suggested approach would be more accurate,
especially in the long run.

 -- Keir

On 15/8/08 19:41, "Beth Kon" <eak@xxxxxxxxxx> wrote:

> Hello. I'm looking over the Xen hpet.c to see what I can steal for the
> qemu implementation I'm working on. (Thank you kindly :-)
> One thing that doesn't make sense to me is why, in hpet_timer_fn, the
> timer is set with:
> set_timer(&h->timers[tn], NOW() + hpet_tick_to_ns(h, period));
> rather than calculating the difference between the final value of the
> comparator (after the time_after loop) and the current time. This is the
> approach used in hpet_set_timer:
> set_timer(&h->timers[tn], NOW() + hpet_tick_to_ns(h, diff));
> and would seem to be the best way to get as close to the desired expire
> time as possible. Can someone explain why the approaches are different
> in these 2 places?

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