Hi Marcelo, sorry for the late review.
Il 08/06/2013 04:00, Marcelo Tosatti ha scritto:
> kvmclock should not count while vm is paused, because:
>
> 1) if the vm is paused for long periods, timekeeping
> math can overflow while converting the (large) clocksource
> delta to nanoseconds.
>
> 2) Users rely on CLOCK_MONOTONIC to count run time, that is,
> time which OS has been in a runnable state (see CLOCK_BOOTTIME).
Do you have any ideas on how to implement CLOCK_BOOTTIME for kvmclock?
I think we need to add more fields for the delta between CLOCK_MONOTONIC
and CLOCK_BOOTTIME.
> Change kvmclock driver so as to save clock value when vm transitions
> from runnable to stopped state, and to restore clock value from stopped
> to runnable transition.
>
> Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
>
> diff --git a/hw/i386/kvm/clock.c b/hw/i386/kvm/clock.c
> index 87d4d0f..7d2d005 100644
> --- a/hw/i386/kvm/clock.c
> +++ b/hw/i386/kvm/clock.c
> @@ -28,38 +28,6 @@ typedef struct KVMClockState {
> bool clock_valid;
> } KVMClockState;
>
> -static void kvmclock_pre_save(void *opaque)
> -{
> - KVMClockState *s = opaque;
> - struct kvm_clock_data data;
> - int ret;
> -
> - if (s->clock_valid) {
> - return;
> - }
> - ret = kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, &data);
> - if (ret < 0) {
> - fprintf(stderr, "KVM_GET_CLOCK failed: %s\n", strerror(ret));
> - data.clock = 0;
> - }
> - s->clock = data.clock;
> - /*
> - * If the VM is stopped, declare the clock state valid to avoid re-reading
> - * it on next vmsave (which would return a different value). Will be reset
> - * when the VM is continued.
> - */
> - s->clock_valid = !runstate_is_running();
> -}
> -
> -static int kvmclock_post_load(void *opaque, int version_id)
> -{
> - KVMClockState *s = opaque;
> - struct kvm_clock_data data;
> -
> - data.clock = s->clock;
> - data.flags = 0;
> - return kvm_vm_ioctl(kvm_state, KVM_SET_CLOCK, &data);
> -}
>
> static void kvmclock_vm_state_change(void *opaque, int running,
> RunState state)
> @@ -70,8 +38,18 @@ static void kvmclock_vm_state_change(void *opaque, int running,
> int ret;
>
> if (running) {
> + struct kvm_clock_data data;
> +
Do we need an "if (!s->clock_valid) return;" here, or an assertion? (Or
alternatively, what happens if s->clock_valid == false?)
> s->clock_valid = false;
>
> + data.clock = s->clock;
> + data.flags = 0;
> + ret = kvm_vm_ioctl(kvm_state, KVM_SET_CLOCK, &data);
> + if (ret < 0) {
> + fprintf(stderr, "KVM_SET_CLOCK failed: %s\n", strerror(ret));
> + abort();
> + }
> +
> if (!cap_clock_ctrl) {
> return;
> }
> @@ -84,6 +62,26 @@ static void kvmclock_vm_state_change(void *opaque, int running,
> return;
> }
> }
> + } else {
> + struct kvm_clock_data data;
> + int ret;
> +
> + if (s->clock_valid) {
> + return;
> + }
> + ret = kvm_vm_ioctl(kvm_state, KVM_GET_CLOCK, &data);
> + if (ret < 0) {
> + fprintf(stderr, "KVM_GET_CLOCK failed: %s\n", strerror(ret));
> + abort();
> + }
> + s->clock = data.clock;
> +
> + /*
> + * If the VM is stopped, declare the clock state valid to
> + * avoid re-reading it on next vmsave (which would return
> + * a different value). Will be reset when the VM is continued.
> + */
> + s->clock_valid = !runstate_is_running();
Here we know that !runstate_is_running() is true (we're in the else
branch of "if (running)") so it can just be "s->clock_valid = true".
This matches the false assignment in the other branch. This is just a
nit, but it makes the code clearer.
Paolo
> }
> }
>
> @@ -100,8 +98,6 @@ static const VMStateDescription kvmclock_vmsd = {
> .version_id = 1,
> .minimum_version_id = 1,
> .minimum_version_id_old = 1,
> - .pre_save = kvmclock_pre_save,
> - .post_load = kvmclock_post_load,
> .fields = (VMStateField[]) {
> VMSTATE_UINT64(clock, KVMClockState),
> VMSTATE_END_OF_LIST()
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