On Tue, Jan 05, 2016 at 05:33:27AM +0300, Dmitry Osipenko wrote:
> ptimer_get_count() might be called while QEMU timer already been expired.
> In that case ptimer would return counter = 0, which might be undesirable
> in case of polled timer. Do counter wrap around for periodic timer to keep
> it distributed.
>
> In addition, there is no reason to keep expired timer tick deferred, so
> just perform the tick from ptimer_get_count().
>
> Signed-off-by: Dmitry Osipenko <dig...@gmail.com>
> ---
> hw/core/ptimer.c | 35 +++++++++++++++++++++++++++++------
> 1 file changed, 29 insertions(+), 6 deletions(-)
>
> diff --git a/hw/core/ptimer.c b/hw/core/ptimer.c
> index 035af97..96a6c7a 100644
> --- a/hw/core/ptimer.c
> +++ b/hw/core/ptimer.c
> @@ -85,15 +85,21 @@ static void ptimer_tick(void *opaque)
>
> uint64_t ptimer_get_count(ptimer_state *s)
> {
> + int enabled = s->enabled;
Variable localisation not needed.
> int64_t now;
> + int64_t next;
> uint64_t counter;
> + int expired;
> + int oneshot;
Variable defs can be localised to the if (enabled) (even though now
in original code doesn't do that).
>
> - if (s->enabled) {
> + if (enabled) {
> now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
> + next = s->next_event;
> + expired = (now - next >= 0);
> + oneshot = (enabled == 2);
> /* Figure out the current counter value. */
This comment is now out of place.
> - if (now - s->next_event > 0
> - || s->period == 0) {
> - /* Prevent timer underflowing if it should already have
> + if (s->period == 0 || (expired && oneshot)) {
> + /* Prevent one-shot timer underflowing if it should already have
> triggered. */
> counter = 0;
> } else {
> @@ -114,12 +120,12 @@ uint64_t ptimer_get_count(ptimer_state *s)
> backwards.
> */
>
> - if ((s->enabled == 1) && (s->limit * period < 10000)) {
> + if (!oneshot && (s->limit * period < 10000)) {
> period = 10000 / s->limit;
> period_frac = 0;
> }
>
> - rem = s->next_event - now;
> + rem = expired ? now - next : next - now;
> div = period;
>
> clz1 = clz64(rem);
> @@ -139,6 +145,23 @@ uint64_t ptimer_get_count(ptimer_state *s)
> div += 1;
> }
> counter = rem / div;
> +
> + if (expired) {
> + /* Wrap around periodic counter. */
> + counter = s->delta = s->limit - counter % s->limit;
Why do you update the delta here?
Also can you just get ptimer_reload to do the modulo math for you? If the
timer is !oneshot and expired, then you call ptimer_reload anyway,
which will update next_event. When the expired test returns false
you can just reliably use the original logic involving now and next.
> + }
> + }
> +
> + if (expired) {
> + if (oneshot) {
This if-else has a lot of common structure with the one above. I think
they could be merged.
Regards,
Peter
> + ptimer_tick(s);
> + } else {
> + /* Don't use ptimer_tick() for the periodic timer since it
> + * would reset the delta value.
> + */
> + ptimer_trigger(s);
> + ptimer_reload(s);
> + }
> }
> } else {
> counter = s->delta;
> --
> 2.6.4
>
