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

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2011-02-07 16:01, Anthony Liguori wrote:
> On 02/07/2011 08:57 AM, Jan Kiszka wrote:
>> There should rather be a special vmstate struct for PeriodicTimer, just
>> like we already have for normal timers.
>>    
> 
> Agreed.
> 
>>> 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.
>>>      
>> I'm still not sure what the device model is supposed to do with that
>> information. I think at could remain private to the PeriodicTimer
>> implementation (unless we want to dump some stats or such).
>>    
> 
> Yeah, I've been thinking about it too and I think I agree with you.
> 
> So here's the new proposal:
> 
> typedef struct PeriodicTimer PeriodicTimer;
> 
> /**
>   * @accumulated_ticks:  the number of unacknowledged ticks in total 
> since the creation of the timer
>   **/
> typedef void (PeriodicTimerFunc)(void *opaque);

Or just use QEMUTimerCB directly. BTW, QEMUPeriodicTimer* would probably
be more consistent with the existing naming scheme.

> 
> PeriodicTimer *periodic_timer_new(PeriodicTimerFunc *cb, void *opaque);
> 
> void periodic_timer_mod(PeriodicTimer *timer, int64_t interval, TimeUnit 
> unit);
> 
> /**
>   * @policy: the drift catch-up policy
>   *                DRIFT_COMP_FAST, deliver next tick as soon as any 
> tick is acknowledged if accumulated_ticks > 1
>   *                DRIFT_COMP_NONE, do not change interval regardless of 
> accumulated ticks
>   *                DRIFT_COMP_GRADUAL, shorten interval by half until 
> accumulated_ticks <= 1
>   */
> void periodic_timer_set_policy(PeriodicTimer *timer, 
> DriftCompensationPolicy policy);
> 
> /**
>   * @ticks: number of ticks to acknowledge that are currently outstanding.
>   **/
> void periodic_timer_ack(PeriodicTimer *timer, int ticks);
> 
> int periodic_timer_get_accumulated_ticks(PeriodicTimer *timer);
> 

Looks like a plan.

Jan

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