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kvm: i8254: Cache kernel clock offset in KVMPITState

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To prepare the final fix for clock calibration issues with the in-kernel
PIT, we want to cache the offset between vmclock and the clock used by
the in-kernel PIT. So far, we only need to update it when the VM state
changes between running and stopped because we only read the in-kernel
PIT state while the VM is running.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Jan Kiszka 2012-08-14 10:24:03 +02:00 committed by Marcelo Tosatti
parent 873359d411
commit 205df4d1a8
1 changed files with 24 additions and 14 deletions
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38
hw/kvm/i8254.c
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@ -35,7 +35,8 @@
typedef struct KVMPITState {
PITCommonState pit;
LostTickPolicy lost_tick_policy;
bool state_valid;
bool vm_stopped;
int64_t kernel_clock_offset;
} KVMPITState;
static int64_t abs64(int64_t v)
@ -43,19 +44,11 @@ static int64_t abs64(int64_t v)
return v < 0 ? -v : v;
}
static void kvm_pit_get(PITCommonState *pit)
static void kvm_pit_update_clock_offset(KVMPITState *s)
{
KVMPITState *s = DO_UPCAST(KVMPITState, pit, pit);
struct kvm_pit_state2 kpit;
struct kvm_pit_channel_state *kchan;
struct PITChannelState *sc;
int64_t offset, clock_offset;
struct timespec ts;
int i, ret;
if (s->state_valid) {
return;
}
int i;
/*
* Measure the delta between CLOCK_MONOTONIC, the base used for
@ -72,6 +65,21 @@ static void kvm_pit_get(PITCommonState *pit)
clock_offset = offset;
}
}
s->kernel_clock_offset = clock_offset;
}
static void kvm_pit_get(PITCommonState *pit)
{
KVMPITState *s = DO_UPCAST(KVMPITState, pit, pit);
struct kvm_pit_state2 kpit;
struct kvm_pit_channel_state *kchan;
struct PITChannelState *sc;
int i, ret;
/* No need to re-read the state if VM is stopped. */
if (s->vm_stopped) {
return;
}
if (kvm_has_pit_state2()) {
ret = kvm_vm_ioctl(kvm_state, KVM_GET_PIT2, &kpit);
@ -106,7 +114,7 @@ static void kvm_pit_get(PITCommonState *pit)
sc->mode = kchan->mode;
sc->bcd = kchan->bcd;
sc->gate = kchan->gate;
sc->count_load_time = kchan->count_load_time + clock_offset;
sc->count_load_time = kchan->count_load_time + s->kernel_clock_offset;
}
sc = &pit->channels[0];
@ -211,10 +219,12 @@ static void kvm_pit_vm_state_change(void *opaque, int running,
KVMPITState *s = opaque;
if (running) {
s->state_valid = false;
kvm_pit_update_clock_offset(s);
s->vm_stopped = false;
} else {
kvm_pit_update_clock_offset(s);
kvm_pit_get(&s->pit);
s->state_valid = true;
s->vm_stopped = true;
}
}