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 ?
I want to enter the KVM code and try to make a REAL_TIME and accurate synchronization between the host and guest clocks .
Currently I don’t see that KVM updates the guest’s clock when I manually set the host’s clock. I don’t see any impact on the guest’s clock Also after booting the guest I see a diff-time of ~1ms between the 2 clocks.
Questions:
- What can you tell about the feasibility of this task ?
- Can you give me a reference/guides for this task’s design ? where to start ? potential problems ? pvclock ? when to update , when reentering the VM ? etc..
(I’m working with kvm-clock as a source clock, my machine is a very modern x86 with full virtualization support, constant TSC etc..) Thanks in adavance Avi
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