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kvm: i8254: Fix conversion of in-kernel to userspace state

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Due to a offset between the clock used to generate the in-kernel
count_load_time (CLOCK_MONOTONIC) and the clock used for processing this
in userspace (vm_clock), reading back the output of PIT channel 2 via
port 0x61 was broken. One use cases that suffered from it was the CPU
frequency calibration of SeaBIOS, which also affected IDE/AHCI timeouts.

This fixes it by calibrating the offset between both clocks on
kvm_pit_get and adjusting the kernel value before saving it in the
userspace state. As the calibration only works while the vm_clock is
running, we cache the in-kernel state across stopped phases.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Jan Kiszka 2012-06-06 16:28:42 +02:00 committed by Avi Kivity
parent 0614cb82ca
commit 0cdd3d1444
1 changed files with 52 additions and 5 deletions
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57
hw/kvm/i8254.c
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@ -23,31 +23,63 @@
* THE SOFTWARE.
*/
#include "qemu-timer.h"
#include "sysemu.h"
#include "hw/i8254.h"
#include "hw/i8254_internal.h"
#include "kvm.h"
#define KVM_PIT_REINJECT_BIT 0
#define CALIBRATION_ROUNDS 3
typedef struct KVMPITState {
PITCommonState pit;
LostTickPolicy lost_tick_policy;
bool state_valid;
} KVMPITState;
static void kvm_pit_get(PITCommonState *s)
static int64_t abs64(int64_t v)
{
return v < 0 ? -v : v;
}
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;
int64_t offset, clock_offset;
struct timespec ts;
int i, ret;
if (s->state_valid) {
return;
}
/*
* Measure the delta between CLOCK_MONOTONIC, the base used for
* kvm_pit_channel_state::count_load_time, and vm_clock. Take the
* minimum of several samples to filter out scheduling noise.
*/
clock_offset = INT64_MAX;
for (i = 0; i < CALIBRATION_ROUNDS; i++) {
offset = qemu_get_clock_ns(vm_clock);
clock_gettime(CLOCK_MONOTONIC, &ts);
offset -= ts.tv_nsec;
offset -= (int64_t)ts.tv_sec * 1000000000;
if (abs64(offset) < abs64(clock_offset)) {
clock_offset = offset;
}
}
if (kvm_has_pit_state2()) {
ret = kvm_vm_ioctl(kvm_state, KVM_GET_PIT2, &kpit);
if (ret < 0) {
fprintf(stderr, "KVM_GET_PIT2 failed: %s\n", strerror(ret));
abort();
}
s->channels[0].irq_disabled = kpit.flags & KVM_PIT_FLAGS_HPET_LEGACY;
pit->channels[0].irq_disabled = kpit.flags & KVM_PIT_FLAGS_HPET_LEGACY;
} else {
/*
* kvm_pit_state2 is superset of kvm_pit_state struct,
@ -61,7 +93,7 @@ static void kvm_pit_get(PITCommonState *s)
}
for (i = 0; i < 3; i++) {
kchan = &kpit.channels[i];
sc = &s->channels[i];
sc = &pit->channels[i];
sc->count = kchan->count;
sc->latched_count = kchan->latched_count;
sc->count_latched = kchan->count_latched;
@ -74,10 +106,10 @@ static void kvm_pit_get(PITCommonState *s)
sc->mode = kchan->mode;
sc->bcd = kchan->bcd;
sc->gate = kchan->gate;
sc->count_load_time = kchan->count_load_time;
sc->count_load_time = kchan->count_load_time + clock_offset;
}
sc = &s->channels[0];
sc = &pit->channels[0];
sc->next_transition_time =
pit_get_next_transition_time(sc, sc->count_load_time);
}
@ -173,6 +205,19 @@ static void kvm_pit_irq_control(void *opaque, int n, int enable)
kvm_pit_put(pit);
}
static void kvm_pit_vm_state_change(void *opaque, int running,
RunState state)
{
KVMPITState *s = opaque;
if (running) {
s->state_valid = false;
} else {
kvm_pit_get(&s->pit);
s->state_valid = true;
}
}
static int kvm_pit_initfn(PITCommonState *pit)
{
KVMPITState *s = DO_UPCAST(KVMPITState, pit, pit);
@ -215,6 +260,8 @@ static int kvm_pit_initfn(PITCommonState *pit)
qdev_init_gpio_in(&pit->dev.qdev, kvm_pit_irq_control, 1);
qemu_add_vm_change_state_handler(kvm_pit_vm_state_change, s);
return 0;
}