On 2011-04-08 17:20, Ulrich Obergfell wrote:
> Loss of periodic timer interrupts caused by delayed callbacks and by
> interrupt coalescing is compensated by gradually injecting additional
> interrupts during subsequent timer intervals, starting at a rate of
> one additional interrupt per interval. If further interrupts are lost
> while compensation is in progress, the rate is increased. A limit is
> imposed on the rate and on the 'backlog' of lost interrupts that are
> to be injected. If a guest o/s modifies the comparator register value
> while compensation is in progress, the 'backlog' of lost interrupts
> that are to be injected is scaled to the new value.
>
> Injecting additional timer interrupts to compensate lost interrupts
> can alleviate long term time drift. However, on a short time scale,
> this method can have the side effect of making virtual machine time
> intermittently pass faster than real time (depending on the guest's
> time keeping algorithm). Compensation is disabled by default and can
> be enabled for guests where this behaviour is acceptable.
>
> Signed-off-by: Ulrich Obergfell <uobergfe@xxxxxxxxxx>
> ---
> hw/hpet.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 files changed, 57 insertions(+), 1 deletions(-)
>
> diff --git a/hw/hpet.c b/hw/hpet.c
> index b5625fb..5a25a96 100644
> --- a/hw/hpet.c
> +++ b/hw/hpet.c
> @@ -42,6 +42,9 @@
>
> #define HPET_MSI_SUPPORT 0
>
> +#define MAX_IRQS_TO_INJECT (uint32_t)5000
> +#define MAX_IRQ_RATE (uint32_t)10
> +
> struct HPETState;
> typedef struct HPETTimer { /* timers */
> uint8_t tn; /*timer number*/
> @@ -309,8 +312,11 @@ static const VMStateDescription vmstate_hpet = {
> static void hpet_timer(void *opaque)
> {
> HPETTimer *t = opaque;
> + HPETState *s = t->state;
> uint64_t diff;
>
> + int irq_delivered = 0;
> + uint32_t irq_count = 0;
> uint64_t period = t->period;
> uint64_t cur_tick = hpet_get_ticks(t->state);
>
> @@ -318,13 +324,36 @@ static void hpet_timer(void *opaque)
> if (t->config & HPET_TN_32BIT) {
> while (hpet_time_after(cur_tick, t->cmp)) {
> t->cmp = (uint32_t)(t->cmp + t->period);
> + irq_count++;
> }
> } else {
> while (hpet_time_after64(cur_tick, t->cmp)) {
> t->cmp += period;
> + irq_count++;
> }
> }
> diff = hpet_calculate_diff(t, cur_tick);
> + if (s->driftfix) {
> + if (t->saved_period != t->period) {
> + uint64_t tmp = (t->irqs_to_inject * t->saved_period)
> + + t->ticks_not_accounted;
> + t->irqs_to_inject = tmp / t->period;
> + t->ticks_not_accounted = tmp % t->period;
> + t->saved_period = t->period;
> + }
> + t->irqs_to_inject += irq_count;
> + t->irqs_to_inject = MIN(t->irqs_to_inject, MAX_IRQS_TO_INJECT);
> + if (t->irqs_to_inject > 1) {
> + if (irq_count > 1) {
> + t->irq_rate++;
> + t->irq_rate = MIN(t->irq_rate, MAX_IRQ_RATE);
> + }
> + if (irq_count || t->divisor == 0) {
> + t->divisor = t->irq_rate;
> + }
> + diff /= t->divisor--;
> + }
> + }
Did I miss some change in the plan? I thought we were heading for a
generic, reusable driftfix tool box (or periodic timer service)? Or is
this intentionally an intermediate step?
> qemu_mod_timer(t->qemu_timer,
> qemu_get_clock(vm_clock) + (int64_t)ticks_to_ns(diff));
> } else if (t->config & HPET_TN_32BIT && !timer_is_periodic(t)) {
> @@ -335,7 +364,22 @@ static void hpet_timer(void *opaque)
> t->wrap_flag = 0;
> }
> }
> - update_irq(t, 1);
> + if (s->driftfix && timer_is_periodic(t) && period != 0) {
> + if (t->irqs_to_inject) {
> + irq_delivered = update_irq(t, 1);
> + if (irq_delivered) {
> + t->irq_rate = MIN(t->irq_rate, t->irqs_to_inject);
> + t->irqs_to_inject--;
> + } else {
> + if (irq_count) {
> + t->irq_rate++;
> + t->irq_rate = MIN(t->irq_rate, MAX_IRQ_RATE);
> + }
> + }
> + }
> + } else {
> + update_irq(t, 1);
> + }
> }
>
> static void hpet_set_timer(HPETTimer *t)
> @@ -674,6 +718,12 @@ static void hpet_reset(DeviceState *d)
> timer->config |= 0x00000004ULL << 32;
> timer->period = 0ULL;
> timer->wrap_flag = 0;
> +
> + timer->saved_period = 0;
> + timer->ticks_not_accounted = 0;
> + timer->irqs_to_inject = 0;
> + timer->irq_rate = 1;
> + timer->divisor = 1;
> }
>
> s->hpet_counter = 0ULL;
> @@ -734,6 +784,12 @@ static int hpet_init(SysBusDevice *dev)
> timer->qemu_timer = qemu_new_timer(vm_clock, hpet_timer, timer);
> timer->tn = i;
> timer->state = s;
> +
> + timer->saved_period = 0;
> + timer->ticks_not_accounted = 0;
> + timer->irqs_to_inject = 0;
> + timer->irq_rate = 1;
> + timer->divisor = 1;
We call reset after initializing devices, at least for cold-plugged ones.
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
--
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
