Re: [Qemu-devel] Re: [RFC: 0/2] patch for QEMU HPET periodic timer emulation to alleviate time drift

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 02/07/2011 08:58 AM, Avi Kivity wrote:
On 02/07/2011 04:54 PM, Anthony Liguori wrote:

  Why the accumulated_ticks argument?

Then the missing ticks is stored in the PeriodicTimer instead of storing it in the device state. That means we won't forget to save it in vmstate.

It's convenient because then if we lose ticks in the PeriodicTimer layer, the devices have instance access to that info. When you do a read() from timerfd, it returns the number of coalesced events. That's the interface I had in my mind.

We could just add a getter for PeriodicTimer and it would serve the same purpose.

If a drift compensation policy is in effect, you don't need the missed ticks, since you will get one callback for each (delayed) tick. If there is no drift compensation policy, presumably you aren't interested in lost ticks. So the ticks argument isn't very useful.

On the other hand, we need a way to inject lost ticks into a PeriodicTimer. If interrupt injection detects that an interrupt was coalesced, we want the timer to schedule a new tick for us.

As an optimization, if you can do something useful with the knowledge that we missed 20 ticks instead of waiting for 20 callbacks, it's useful to have. But adding a getter makes that possible and I agree that it clutters the interface for an edge use-case.

Regards,

Anthony Liguori


--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html


[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]
  Powered by Linux