diff mbox

[3/5] mc146818rtc: properly count the time for the next interrupt

Message ID 20170412095111.11728-4-xiaoguangrong@tencent.com (mailing list archive)
State New, archived
Headers show

Commit Message

Xiao Guangrong April 12, 2017, 9:51 a.m. UTC 
From: Tai Yunfang <yunfangtai@tencent.com>

If periodic_timer_update() is called due to RegA reconfiguration, i.e,
the period is updated, current time is not the start point for the next
periodic timer, instead, which should start from the last interrupt,
otherwise, the clock in VM will become slow

This patch takes the clocks from last interrupt to current clock into
account and compensates the clocks for the next interrupt, especially，
if a complete interrupt was lost in this window, the time can be caught
up by LOST_TICK_POLICY_SLEW

[ Xiao: redesign the algorithm based on Yunfang's original work. ]

Signed-off-by: Tai Yunfang <yunfangtai@tencent.com>
Signed-off-by: Xiao Guangrong <xiaoguangrong@tencent.com>
---
 hw/timer/mc146818rtc.c | 71 +++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 64 insertions(+), 7 deletions(-)

Comments

Paolo Bonzini May 3, 2017, 3:32 p.m. UTC | #1 
On 12/04/2017 11:51, guangrong.xiao@gmail.com wrote:
> +#ifdef TARGET_I386
> +            /*
> +             * if more than period clocks were passed, i.e, the timer interrupt
> +             * has been lost, we should catch up the time.
> +             */
> +            if (s->lost_tick_policy == LOST_TICK_POLICY_SLEW &&
> +                (lost_clock / period)) {
> +                int lost_interrupt = lost_clock / period;
> +
> +                s->irq_coalesced += lost_interrupt;
> +                lost_clock -= lost_interrupt * period;
> +                if (lost_interrupt) {
> +                    DPRINTF_C("cmos: compensate %d interrupts, coalesced irqs "
> +                              "increased to %d\n", lost_interrupt,
> +                              s->irq_coalesced);
> +                    rtc_coalesced_timer_update(s);
> +                }

I think you should merge these two patches, since both of them
essentially update the number of coalesced ticks and then split it
between s->irq_coalesced and lost_clock.

Paolo

> +            } else
> +#endif
> +            /*
> +             * no way to compensate the interrupt if LOST_TICK_POLICY_SLEW
> +             * is not used, we should make the time progress anyway.
> +             */
> +            lost_clock = MIN(lost_clock, period);
> +            assert(lost_clock >= 0);
> +        }
> +
Xiao Guangrong May 4, 2017, 2:54 a.m. UTC | #2 
On 05/03/2017 11:32 PM, Paolo Bonzini wrote:
> On 12/04/2017 11:51, guangrong.xiao@gmail.com wrote:
>> +#ifdef TARGET_I386
>> +            /*
>> +             * if more than period clocks were passed, i.e, the timer interrupt
>> +             * has been lost, we should catch up the time.
>> +             */
>> +            if (s->lost_tick_policy == LOST_TICK_POLICY_SLEW &&
>> +                (lost_clo / period)) {
>> +                int lost_interrupt = lost_clock / period;
>> +
>> +                s->irq_coalesced += lost_interrupt;
>> +                lost_clock -= lost_interrupt * period;
>> +                if (lost_interrupt) {
>> +                    DPRINTF_C("cmos: compensate %d interrupts, coalesced irqs "
>> +                              "increased to %d\n", lost_interrupt,
>> +                              s->irq_coalesced);
>> +                    rtc_coalesced_timer_update(s);
>> +                }
> 
> I think you should merge these two patches, since both of them
> essentially update the number of coalesced ticks and then split it
> between s->irq_coalesced and lost_clock.

I thought these two patches fix two different issues, one for clock
lost for coalesced-irq and another for period reconfiguration. Your
suggestion sounds reasonable indeed, will merged them in the next
version. :)
Paolo Bonzini May 4, 2017, 12:02 p.m. UTC | #3 
On 04/05/2017 04:54, Xiao Guangrong wrote:
>>>
>>> +            /*
>>> +             * if more than period clocks were passed, i.e, the
>>> timer interrupt
>>> +             * has been lost, we should catch up the time.
>>> +             */
>>> +            if (s->lost_tick_policy == LOST_TICK_POLICY_SLEW &&
>>> +                (lost_clo / period)) {
>>> +                int lost_interrupt = lost_clock / period;
>>> +
>>> +                s->irq_coalesced += lost_interrupt;
>>> +                lost_clock -= lost_interrupt * period;
>>> +                if (lost_interrupt) {
>>> +                    DPRINTF_C("cmos: compensate %d interrupts,
>>> coalesced irqs "
>>> +                              "increased to %d\n", lost_interrupt,
>>> +                              s->irq_coalesced);
>>> +                    rtc_coalesced_timer_update(s);
>>> +                }
>>
>> I think you should merge these two patches, since both of them
>> essentially update the number of coalesced ticks and then split it
>> between s->irq_coalesced and lost_clock.
> 
> I thought these two patches fix two different issues, one for clock
> lost for coalesced-irq and another for period reconfiguration. Your
> suggestion sounds reasonable indeed, will merged them in the next
> version. :)

Yunfang's patch in turn has two parts, one that is only for SLEW and one
that is not.  You can keep the first separate, and merge the second with
yours.

Paolo
diff mbox

Patch

diff --git a/hw/timer/mc146818rtc.c b/hw/timer/mc146818rtc.c
index 649678c..3bf559d 100644
--- a/hw/timer/mc146818rtc.c
+++ b/hw/timer/mc146818rtc.c
@@ -161,8 +161,12 @@  static int period_code_to_clock(int period_code)
     return 1 << (period_code - 1);
 }
 
-/* handle periodic timer */
-static void periodic_timer_update(RTCState *s, int64_t current_time)
+/*
+ * handle periodic timer. @old_period indicates the periodic timer update
+ * is just due to period adjustment.
+ */
+static void
+periodic_timer_update(RTCState *s, int64_t current_time, int old_period)
 {
     int period_code, period;
     int64_t cur_clock, next_irq_clock, lost_clock = 0;
@@ -193,6 +197,56 @@  static void periodic_timer_update(RTCState *s, int64_t current_time)
         cur_clock =
             muldiv64(current_time, RTC_CLOCK_RATE, NANOSECONDS_PER_SECOND);
 
+        /*
+        * if the periodic timer's update is due to period re-configuration,
+        * we should count the clock since last interrupt.
+        */
+        if (old_period) {
+            int64_t last_periodic_clock;
+
+            last_periodic_clock = muldiv64(s->next_periodic_time,
+                                    RTC_CLOCK_RATE, NANOSECONDS_PER_SECOND);
+            /*
+             * if the next interrupt has not happened yet, we recall the last
+             * interrupt based on the original period.
+             */
+            if (last_periodic_clock > cur_clock) {
+                last_periodic_clock -= period_code_to_clock(old_period);
+
+                /* the last interrupt must have happened. */
+                assert(cur_clock >= last_periodic_clock);
+            }
+
+            /* calculate the clock since last interrupt. */
+            lost_clock += cur_clock - last_periodic_clock;
+
+#ifdef TARGET_I386
+            /*
+             * if more than period clocks were passed, i.e, the timer interrupt
+             * has been lost, we should catch up the time.
+             */
+            if (s->lost_tick_policy == LOST_TICK_POLICY_SLEW &&
+                (lost_clock / period)) {
+                int lost_interrupt = lost_clock / period;
+
+                s->irq_coalesced += lost_interrupt;
+                lost_clock -= lost_interrupt * period;
+                if (lost_interrupt) {
+                    DPRINTF_C("cmos: compensate %d interrupts, coalesced irqs "
+                              "increased to %d\n", lost_interrupt,
+                              s->irq_coalesced);
+                    rtc_coalesced_timer_update(s);
+                }
+            } else
+#endif
+            /*
+             * no way to compensate the interrupt if LOST_TICK_POLICY_SLEW
+             * is not used, we should make the time progress anyway.
+             */
+            lost_clock = MIN(lost_clock, period);
+            assert(lost_clock >= 0);
+        }
+
         next_irq_clock = cur_clock + period - lost_clock;
         s->next_periodic_time = muldiv64(next_irq_clock, NANOSECONDS_PER_SECOND,
                                          RTC_CLOCK_RATE) + 1;
@@ -209,7 +263,7 @@  static void rtc_periodic_timer(void *opaque)
 {
     RTCState *s = opaque;
 
-    periodic_timer_update(s, s->next_periodic_time);
+    periodic_timer_update(s, s->next_periodic_time, 0);
     s->cmos_data[RTC_REG_C] |= REG_C_PF;
     if (s->cmos_data[RTC_REG_B] & REG_B_PIE) {
         s->cmos_data[RTC_REG_C] |= REG_C_IRQF;
@@ -428,6 +482,7 @@  static void cmos_ioport_write(void *opaque, hwaddr addr,
                               uint64_t data, unsigned size)
 {
     RTCState *s = opaque;
+    int cur_period;
     bool update_periodic_timer;
 
     if ((addr & 1) == 0) {
@@ -461,6 +516,7 @@  static void cmos_ioport_write(void *opaque, hwaddr addr,
             }
             break;
         case RTC_REG_A:
+            cur_period = s->cmos_data[RTC_REG_A] & 0xf;
             update_periodic_timer = rtc_periodic_timer_updated_by_regA(s, data);
 
             if ((data & 0x60) == 0x60) {
@@ -487,7 +543,8 @@  static void cmos_ioport_write(void *opaque, hwaddr addr,
                 (s->cmos_data[RTC_REG_A] & REG_A_UIP);
 
             if (update_periodic_timer) {
-                periodic_timer_update(s, qemu_clock_get_ns(rtc_clock));
+                periodic_timer_update(s, qemu_clock_get_ns(rtc_clock),
+                                      cur_period);
             }
 
             check_update_timer(s);
@@ -523,7 +580,7 @@  static void cmos_ioport_write(void *opaque, hwaddr addr,
             s->cmos_data[RTC_REG_B] = data;
 
             if (update_periodic_timer) {
-                periodic_timer_update(s, qemu_clock_get_ns(rtc_clock));
+                periodic_timer_update(s, qemu_clock_get_ns(rtc_clock), 0);
             }
 
             check_update_timer(s);
@@ -793,7 +850,7 @@  static int rtc_post_load(void *opaque, int version_id)
         uint64_t now = qemu_clock_get_ns(rtc_clock);
         if (now < s->next_periodic_time ||
             now > (s->next_periodic_time + get_max_clock_jump())) {
-            periodic_timer_update(s, qemu_clock_get_ns(rtc_clock));
+            periodic_timer_update(s, qemu_clock_get_ns(rtc_clock), 0);
         }
     }
 
@@ -858,7 +915,7 @@  static void rtc_notify_clock_reset(Notifier *notifier, void *data)
     int64_t now = *(int64_t *)data;
 
     rtc_set_date_from_host(ISA_DEVICE(s));
-    periodic_timer_update(s, now);
+    periodic_timer_update(s, now, 0);
     check_update_timer(s);
 #ifdef TARGET_I386
     if (s->lost_tick_policy == LOST_TICK_POLICY_SLEW) {