On Mon, Jan 13, 2020 at 1:43 PM Peter Zijlstra [off-list ref] wrote:

On Mon, Jan 13, 2020 at 11:43:18AM +0000, Singh, Balbir wrote:

quoted

For your original comment, just wanted to clarify the following:

1. After hibernation, the machine can be resumed on a different but compatible
host (these are VM images hibernated)
2. This means the clock between host1 and host2 can/will be different

In your comments are you making the assumption that the host(s) is/are the
same? Just checking the assumptions being made and being on the same page with
them.

I would expect this to be the same problem we have as regular suspend,
after power off the TSC will have been reset, so resume will have to
somehow bridge that gap. I've no idea if/how it does that.

In general, this is done by timekeeping_resume() and the only special
thing done for the TSC appears to be the tsc_verify_tsc_adjust(true)
call in tsc_resume().

I remember some BIOSes had crazy TSC ideas for suspend2ram, and we grew
tsc_restore_sched_clock_state() for it.

Playing crazy games like what you're doing just isn't it though.

Right.