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diff --git a/sys/amd64/vmm/io/vrtc.c b/sys/amd64/vmm/io/vrtc.c
--- a/sys/amd64/vmm/io/vrtc.c
+++ b/sys/amd64/vmm/io/vrtc.c
@@ -80,6 +80,7 @@
u_int addr; /* RTC register to read or write */
sbintime_t base_uptime;
time_t base_rtctime;
+ sbintime_t callout_time;
struct rtcdev rtcdev;
};
@@ -520,8 +521,9 @@
}
static void
-vrtc_callout_reset(struct vrtc *vrtc, sbintime_t freqsbt)
+vrtc_callout_reset(struct vrtc *vrtc, sbintime_t freqsbt, bool periodic)
{
+ sbintime_t now;
KASSERT(VRTC_LOCKED(vrtc), ("%s: vrtc not locked", __func__));
@@ -533,8 +535,20 @@
return;
}
VM_CTR1(vrtc->vm, "RTC callout frequency %d hz", SBT_1S / freqsbt);
- callout_reset_sbt(&vrtc->callout, freqsbt, 0, vrtc_callout_handler,
- vrtc, 0);
+
+ /*
+ * From the handler, the next deadline is one period after the previous
+ * one, not one period after the handler ran: else the latency of each
+ * callout adds up and the interrupt comes at a lower rate than the
+ * guest programmed. Start afresh if that deadline has passed.
+ */
+ now = sbinuptime();
+ if (periodic)
+ vrtc->callout_time += freqsbt;
+ if (!periodic || vrtc->callout_time < now)
+ vrtc->callout_time = now + freqsbt;
+ callout_reset_sbt(&vrtc->callout, vrtc->callout_time, 0,
+ vrtc_callout_handler, vrtc, C_ABSOLUTE);
}
static void
@@ -571,7 +585,7 @@
freqsbt = vrtc_freq(vrtc);
KASSERT(freqsbt != 0, ("%s: vrtc frequency cannot be zero", __func__));
- vrtc_callout_reset(vrtc, freqsbt);
+ vrtc_callout_reset(vrtc, freqsbt, true);
done:
VRTC_UNLOCK(vrtc);
}
@@ -690,7 +704,7 @@
*/
newfreq = vrtc_freq(vrtc);
if (newfreq != oldfreq)
- vrtc_callout_reset(vrtc, newfreq);
+ vrtc_callout_reset(vrtc, newfreq, false);
else
vrtc_callout_check(vrtc, newfreq);
@@ -742,7 +756,7 @@
*/
newfreq = vrtc_freq(vrtc);
if (newfreq != oldfreq)
- vrtc_callout_reset(vrtc, newfreq);
+ vrtc_callout_reset(vrtc, newfreq, false);
else
vrtc_callout_check(vrtc, newfreq);
}
@@ -1066,7 +1080,7 @@
SNAPSHOT_BUF_OR_LEAVE(vrtc->rtcdev.nvram2, sizeof(vrtc->rtcdev.nvram2),
meta, ret, done);
- vrtc_callout_reset(vrtc, vrtc_freq(vrtc));
+ vrtc_callout_reset(vrtc, vrtc_freq(vrtc), false);
done:
VRTC_UNLOCK(vrtc);

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