[Xen-devel] [PATCH 3/4] x86/hvm: Avoid needlessly resetting the periodic timer.

[Tim Deegan <tim@xxxxxxx>]

Signed-off-by: Tim Deegan <tim@xxxxxxx>
---
 xen/arch/x86/hvm/rtc.c        |   15 +++++++++++++--
 xen/include/asm-x86/hvm/vpt.h |   11 ++++++-----
 2 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/hvm/rtc.c b/xen/arch/x86/hvm/rtc.c
index 710ae89..ecc9916 100644
--- a/xen/arch/x86/hvm/rtc.c
+++ b/xen/arch/x86/hvm/rtc.c
@@ -78,7 +78,10 @@ void rtc_periodic_interrupt(void *opaque)
 
     spin_lock(&s->lock);
     if ( s->hw.cmos_data[RTC_REG_C] & RTC_PF )
+    {
         destroy_periodic_time(&s->pt);
+        s->pt_active = 0;
+    }
     else
     {
         s->hw.cmos_data[RTC_REG_C] |= RTC_PF;
@@ -109,13 +112,20 @@ static void rtc_timer_update(RTCState *s)
         {
             period = 1 << (period_code - 1); /* period in 32 Khz cycles */
             period = DIV_ROUND(period * 1000000000ULL, 32768); /* in ns */
-            delta = period - ((NOW() - s->start_time) % period);
-            create_periodic_time(v, &s->pt, delta, period, RTC_IRQ, NULL, s);
+            if ( !s->pt_active || (period != s->period) )
+            {
+                s->period = period;
+                s->pt_active = 1;
+                delta = period - ((NOW() - s->start_time) % period);
+                create_periodic_time(v, &s->pt, delta, period,
+                                     RTC_IRQ, NULL, s);
+            }
             break;
         }
         /* fall through */
     default:
         destroy_periodic_time(&s->pt);
+        s->pt_active = 0;
         break;
     }
 }
@@ -717,6 +727,7 @@ void rtc_reset(struct domain *d)
     RTCState *s = domain_vrtc(d);
 
     destroy_periodic_time(&s->pt);
+    s->pt_active = 0;
     s->pt.source = PTSRC_isa;
 }
 
diff --git a/xen/include/asm-x86/hvm/vpt.h b/xen/include/asm-x86/hvm/vpt.h
index 2e9c7d2..76a83a1 100644
--- a/xen/include/asm-x86/hvm/vpt.h
+++ b/xen/include/asm-x86/hvm/vpt.h
@@ -104,16 +104,17 @@ typedef struct RTCState {
     struct hvm_hw_rtc hw;
     /* RTC's idea of the current time */
     struct tm current_tm;
-    /* periodic timer */
-    s_time_t start_time;
-    /* second update */
-    struct periodic_time pt;
     /* update-ended timer */
     struct timer update_timer;
     struct timer update_timer2;
+    uint64_t next_update_time;
     /* alarm timer */
     struct timer alarm_timer;
-    uint64_t next_update_time;
+    /* periodic timer */
+    struct periodic_time pt;
+    s_time_t start_time;
+    int period;
+    bool_t pt_active;
     uint32_t use_timer;
     spinlock_t lock;
 } RTCState;
-- 
1.7.10.4


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