Re: [Qemu-devel] [PATCH v2 3/5] hpet 'driftfix': add fields to HPETTimer and VMStateDescription

[Ulrich Obergfell]

>> vmstate_hpet_timer = {
>>           VMSTATE_UINT64(fsb, HPETTimer),
>>           VMSTATE_UINT64(period, HPETTimer),
>>           VMSTATE_UINT8(wrap_flag, HPETTimer),
>> + VMSTATE_UINT64_V(saved_period, HPETTimer, 3),
>> + VMSTATE_UINT64_V(ticks_not_accounted, HPETTimer, 3),
>> + VMSTATE_UINT32_V(irqs_to_inject, HPETTimer, 3),
>> + VMSTATE_UINT32_V(irq_rate, HPETTimer, 3),
>> + VMSTATE_UINT32_V(divisor, HPETTimer, 3),
>
> We ought to be able to use a subsection keyed off of whether any ticks
> are currently accumulated, no?


Anthony,

I'm not sure if I understand your question correctly. Are you suggesting
to migrate the driftfix-related state conditionally / only if there are
any ticks accumulated in 'ticks_not_accounted' and 'irqs_to_inject' ?

The size of the driftfix-related state is 28 bytes per timer and we have
32 timers per HPETState, i.e. 896 additional bytes per HPETState. With a
maximum number of 8 HPET blocks (HPETState), this amounts to 7168 bytes.
Hence, unconditional migration of the driftfix-related state should not
cause significant additional overhead.

Maybe I missed something. Could you please explain which benefit you see
in using a subsection ?


Regards,

Uli