2016-04-06 13:51+0000, Avi Cohen:
>> 2016-04-05 15:07+0000, Avi Cohen:
>> > What do you think about this simple solution:
>> > Currently the KVM updates the system-time in the structure
>> > pvclock_vcpu_time_info in the guest memory with the MONOTONIC time
>> struct pvclock_vcpu_time_info {
>> > u32 version;
>> > u32 pad0;
>> > u64 tsc_timestamp;
>> > u64 system_time;
>> > u32 tsc_to_system_mul;
>> > s8 tsc_shift;
>> > u8 flags;
>> > u8 pad[2];
>> > } __attribute__((__packed__));
>> >
>> > This is the default kvm-clcok.
>> > I think to add another clock source named - kvm-clock-realtime, and to update
>> system_time with host's REAL_TIME clock.
>> > What is your opinion ?
>>
>> Would you be ok with a wall_time entry in pvclock_vcpu_time_info that would
>> tell the host real time at system_time?
>> struct pvclock_wall_clock should say the host real time when system_time was
>> 0, so it's the same. wallclock = CLOCK_REALTIME, most likely.
>>
>> Creating a new clock would allow us to get rid of many other problems, but your
>> goal might be achievable with existing interfaces.
>>
>
> Yes - it will be ok to update the pvclock_wall_clock with the host CLOCK_REALTIME.
> But I think I also need the guest's TSC at that time of update,
> struct pvclock_wall_clock {
> 37 u32 version;
> 38 u32 sec;
> 39 u32 nsec;
> New field tsc_timestamp;
> New field tsc_to_system_mul;
> 40 } __attribute__((__packed__));
>
> Now the guest - when need to read the current time - can do something like this :
> Current_time = sec * sec_to_nano + nsec + (rdtdc () - tsc_timestamp) * tsc_to_system_mul
No need. pvclock_wall_clock.{sec,nsec} is synchronized with system_time
and system_time is synchronized with TSC. To get the current real time,
you just add times from pvclock_vcpu_time_info, pvclock_wall_clock and
TSC, like kvm_get_wallclock() does.
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