Re: [Qemu-devel] [qemu patch V4 2/2] kvmclock: reduce kvmclock difference on migration

[Marcelo Tosatti <mtosatti@redhat.com>]

On Mon, Dec 12, 2016 at 04:01:05PM -0200, Eduardo Habkost wrote:
> On Sat, Dec 10, 2016 at 03:21:50PM -0200, Marcelo Tosatti wrote:
> [...]
> >  static void kvmclock_realize(DeviceState *dev, Error **errp)
> >  {
> >      KVMClockState *s = KVM_CLOCK(dev);
> >  
> > +    if (kvm_has_adjust_clock_stable()) {
> > +        s->clock_is_reliable = true;
> > +    }
> > +
> 
> This seems unnecessary, as kvmclock_vm_state_change() makes sure
> it is set at the same time as s->clock. Should we just remove it?

There is this initialization that goes from ~running -> running
which assumes its initialized:

static void kvmclock_vm_state_change(void *opaque, int running,
                                     RunState state)
{
    KVMClockState *s = opaque;
    CPUState *cpu;
    int cap_clock_ctrl = kvm_check_extension(kvm_state,
KVM_CAP_KVMCLOCK_CTRL);
    int ret;

    if (running) {
        struct kvm_clock_data data = {};
        uint64_t pvclock_via_mem = 0;

        /*
         * If the host where s->clock was read did not support reliable
         * KVM_GET_CLOCK, read kvmclock value from memory.
         */
        if (!s->clock_is_reliable) {
            pvclock_via_mem = kvmclock_current_nsec(s);
        }