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

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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);

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);

Regards,

Anthony Liguori

Jan


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