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

[Jan Kiszka]

On 2011-02-07 15:28, Anthony Liguori wrote:
> On 02/07/2011 08:10 AM, Jan Kiszka wrote:
>> Again: please not in an ad-hoc fashion but as a generic services usable
>> by _all_ periodic timer sources that want to implement compensation.
>> This infrastructure should also be designed to once integrate IRQ
>> coalescing information as well.
>>
>> The point why I'm insisting on a broader solution is that both sources
>> for lost ticks (iothread and vcpu) end up in the same output: an
>> adjustment of the injection frequency of the affected timer device.
>> There is not "HPET" or "RTC" or "PIT" in this, all this may apply to the
>> SoC timer of some emulated ARM board as well.
>>    
> 
> Fair enough, how about:
> 
> typedef struct PeriodicTimer PeriodicTimer;
> 
> /**
>   * @accumulated_ticks:  the number of unacknowledged ticks in total 
> since the creation of the timer
>   **/
> typedef void (PeriodicTimer)(void *opaque, int accumulated_ticks);

I guess you mean PeriodicTimerFunc. Why the accumulated_ticks argument?

> 
> 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);
> 

Looks reasonable otherwise.

Jan

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