Improve guest time keeping
Even though we accounted for lost ticks, the accounting was not precise.
Specifically, we didn''t account for the delay in calling the ac_timer
handler.
Signed-off-by: Eddie Dong <eddie.dong@intel.com>
Signed-off-by: Arun Sharma <arun.sharma@intel.com>
diff -r d016dd226b0d -r 83180ee86481 xen/arch/x86/vmx_intercept.c
--- a/xen/arch/x86/vmx_intercept.c Mon Jul 18 23:15:02 2005
+++ b/xen/arch/x86/vmx_intercept.c Mon Jul 18 23:47:48 2005
@@ -197,12 +197,23 @@
static void pit_timer_fn(void *data)
{
struct vmx_virpit_t *vpit = data;
+ s_time_t next;
+ int missed_ticks;
+
+ missed_ticks = (NOW() - vpit->scheduled) / MILLISECS(vpit->period);
/* Set the pending intr bit, and send evtchn notification to myself. */
if (test_and_set_bit(vpit->vector, vpit->intr_bitmap))
vpit->pending_intr_nr++; /* already set, then count the pending intr
*/
- set_ac_timer(&vpit->pit_timer, NOW() + MILLISECS(vpit->period));
+ /* pick up missed timer tick */
+ if ( missed_ticks > 0 ) {
+ vpit->pending_intr_nr+= missed_ticks;
+ vpit->scheduled += missed_ticks * MILLISECS(vpit->period);
+ }
+ next = vpit->scheduled + MILLISECS(vpit->period);
+ set_ac_timer(&vpit->pit_timer, next);
+ vpit->scheduled = next;
}
@@ -263,7 +274,8 @@
vpit->intr_bitmap = intr;
- set_ac_timer(&vpit->pit_timer, NOW() + MILLISECS(vpit->period));
+ vpit->scheduled = NOW() + MILLISECS(vpit->period);
+ set_ac_timer(&vpit->pit_timer, vpit->scheduled);
/*restore the state*/
p->state = STATE_IORESP_READY;
diff -r d016dd226b0d -r 83180ee86481 xen/include/asm-x86/vmx_virpit.h
--- a/xen/include/asm-x86/vmx_virpit.h Mon Jul 18 23:15:02 2005
+++ b/xen/include/asm-x86/vmx_virpit.h Mon Jul 18 23:47:48 2005
@@ -19,6 +19,7 @@
/* for simulation of counter 0 in mode 2*/
int vector; /* the pit irq vector */
unsigned int period; /* the frequency. e.g. 10ms*/
+ s_time_t scheduled; /* scheduled timer interrupt */
unsigned int channel; /* the pit channel, counter 0~2 */
u64 *intr_bitmap;
unsigned int pending_intr_nr; /* the couner for pending timer interrupts */
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