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RTC: Do not fire timer periodically to catch next alarm

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This patch limits further the usage of a periodic timer.  It computes the
time of the next alarm, and uses it to skip all intermediate occurrences
of the timer.

Cc: Yang Zhang <yang.z.zhang@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
This commit is contained in:
Paolo Bonzini 2012-08-02 18:04:11 +02:00 committed by Anthony Liguori
parent 41a9b8b24d
commit 00cf57747d
1 changed files with 104 additions and 15 deletions
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119
hw/mc146818rtc.c
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@ -46,6 +46,11 @@
#endif
#define NSEC_PER_SEC 1000000000LL
#define SEC_PER_MIN 60
#define MIN_PER_HOUR 60
#define SEC_PER_HOUR 3600
#define HOUR_PER_DAY 24
#define SEC_PER_DAY 86400
#define RTC_REINJECT_ON_ACK_COUNT 20
#define RTC_CLOCK_RATE 32768
@ -69,6 +74,7 @@ typedef struct RTCState {
int64_t next_periodic_time;
/* update-ended timer */
QEMUTimer *update_timer;
uint64_t next_alarm_time;
uint16_t irq_reinject_on_ack_count;
uint32_t irq_coalesced;
uint32_t period;
@ -82,6 +88,7 @@ static void rtc_set_time(RTCState *s);
static void rtc_update_time(RTCState *s);
static void rtc_set_cmos(RTCState *s);
static inline int rtc_from_bcd(RTCState *s, int a);
static uint64_t get_next_alarm(RTCState *s);
static inline bool rtc_running(RTCState *s)
{
@ -204,6 +211,7 @@ static void check_update_timer(RTCState *s)
{
uint64_t next_update_time;
uint64_t guest_nsec;
int next_alarm_sec;
/* From the data sheet: "Holding the dividers in reset prevents
* interrupts from operating, while setting the SET bit allows"
@ -226,9 +234,21 @@ static void check_update_timer(RTCState *s)
}
guest_nsec = get_guest_rtc_ns(s) % NSEC_PER_SEC;
/* reprogram to next second */
/* if UF is clear, reprogram to next second */
next_update_time = qemu_get_clock_ns(rtc_clock)
+ NSEC_PER_SEC - guest_nsec;
/* Compute time of next alarm. One second is already accounted
* for in next_update_time.
*/
next_alarm_sec = get_next_alarm(s);
s->next_alarm_time = next_update_time + (next_alarm_sec - 1) * NSEC_PER_SEC;
if (s->cmos_data[RTC_REG_C] & REG_C_UF) {
/* UF is set, but AF is clear. Program the timer to target
* the alarm time. */
next_update_time = s->next_alarm_time;
}
if (next_update_time != qemu_timer_expire_time_ns(s->update_timer)) {
qemu_mod_timer(s->update_timer, next_update_time);
}
@ -245,31 +265,95 @@ static inline uint8_t convert_hour(RTCState *s, uint8_t hour)
return hour;
}
static uint32_t check_alarm(RTCState *s)
static uint64_t get_next_alarm(RTCState *s)
{
uint8_t alarm_hour, alarm_min, alarm_sec;
uint8_t cur_hour, cur_min, cur_sec;
int32_t alarm_sec, alarm_min, alarm_hour, cur_hour, cur_min, cur_sec;
int32_t hour, min, sec;
rtc_update_time(s);
alarm_sec = rtc_from_bcd(s, s->cmos_data[RTC_SECONDS_ALARM]);
alarm_min = rtc_from_bcd(s, s->cmos_data[RTC_MINUTES_ALARM]);
alarm_hour = rtc_from_bcd(s, s->cmos_data[RTC_HOURS_ALARM]);
alarm_hour = convert_hour(s, alarm_hour);
alarm_hour = alarm_hour == -1 ? -1 : convert_hour(s, alarm_hour);
cur_sec = rtc_from_bcd(s, s->cmos_data[RTC_SECONDS]);
cur_min = rtc_from_bcd(s, s->cmos_data[RTC_MINUTES]);
cur_hour = rtc_from_bcd(s, s->cmos_data[RTC_HOURS]);
cur_hour = convert_hour(s, cur_hour);
if (((s->cmos_data[RTC_SECONDS_ALARM] & 0xc0) == 0xc0
|| alarm_sec == cur_sec) &&
((s->cmos_data[RTC_MINUTES_ALARM] & 0xc0) == 0xc0
|| alarm_min == cur_min) &&
((s->cmos_data[RTC_HOURS_ALARM] & 0xc0) == 0xc0
|| alarm_hour == cur_hour)) {
return 1;
}
return 0;
if (alarm_hour == -1) {
alarm_hour = cur_hour;
if (alarm_min == -1) {
alarm_min = cur_min;
if (alarm_sec == -1) {
alarm_sec = cur_sec + 1;
} else if (cur_sec > alarm_sec) {
alarm_min++;
}
} else if (cur_min == alarm_min) {
if (alarm_sec == -1) {
alarm_sec = cur_sec + 1;
} else {
if (cur_sec > alarm_sec) {
alarm_hour++;
}
}
if (alarm_sec == SEC_PER_MIN) {
/* wrap to next hour, minutes is not in don't care mode */
alarm_sec = 0;
alarm_hour++;
}
} else if (cur_min > alarm_min) {
alarm_hour++;
}
} else if (cur_hour == alarm_hour) {
if (alarm_min == -1) {
alarm_min = cur_min;
if (alarm_sec == -1) {
alarm_sec = cur_sec + 1;
} else if (cur_sec > alarm_sec) {
alarm_min++;
}
if (alarm_sec == SEC_PER_MIN) {
alarm_sec = 0;
alarm_min++;
}
/* wrap to next day, hour is not in don't care mode */
alarm_min %= MIN_PER_HOUR;
} else if (cur_min == alarm_min) {
if (alarm_sec == -1) {
alarm_sec = cur_sec + 1;
}
/* wrap to next day, hours+minutes not in don't care mode */
alarm_sec %= SEC_PER_MIN;
}
}
/* values that are still don't care fire at the next min/sec */
if (alarm_min == -1) {
alarm_min = 0;
}
if (alarm_sec == -1) {
alarm_sec = 0;
}
/* keep values in range */
if (alarm_sec == SEC_PER_MIN) {
alarm_sec = 0;
alarm_min++;
}
if (alarm_min == MIN_PER_HOUR) {
alarm_min = 0;
alarm_hour++;
}
alarm_hour %= HOUR_PER_DAY;
hour = alarm_hour - cur_hour;
min = hour * MIN_PER_HOUR + alarm_min - cur_min;
sec = min * SEC_PER_MIN + alarm_sec - cur_sec;
return sec <= 0 ? sec + SEC_PER_DAY : sec;
}
static void rtc_update_timer(void *opaque)
@ -284,12 +368,13 @@ static void rtc_update_timer(void *opaque)
rtc_update_time(s);
s->cmos_data[RTC_REG_A] &= ~REG_A_UIP;
if (check_alarm(s)) {
if (qemu_get_clock_ns(rtc_clock) >= s->next_alarm_time) {
irqs |= REG_C_AF;
if (s->cmos_data[RTC_REG_B] & REG_B_AIE) {
qemu_system_wakeup_request(QEMU_WAKEUP_REASON_RTC);
}
}
new_irqs = irqs & ~s->cmos_data[RTC_REG_C];
s->cmos_data[RTC_REG_C] |= irqs;
if ((new_irqs & s->cmos_data[RTC_REG_B]) != 0) {
@ -407,6 +492,9 @@ static inline int rtc_to_bcd(RTCState *s, int a)
static inline int rtc_from_bcd(RTCState *s, int a)
{
if ((a & 0xc0) == 0xc0) {
return -1;
}
if (s->cmos_data[RTC_REG_B] & REG_B_DM) {
return a;
} else {
@ -642,6 +730,7 @@ static const VMStateDescription vmstate_rtc = {
VMSTATE_UINT64_V(last_update, RTCState, 3),
VMSTATE_INT64_V(offset, RTCState, 3),
VMSTATE_TIMER_V(update_timer, RTCState, 3),
VMSTATE_UINT64_V(next_alarm_time, RTCState, 3),
VMSTATE_END_OF_LIST()
}
};