On Mon, 1 Oct 2018, Eric W. Biederman wrote: > In the context of process migration there is a simpler subproblem that I > think it is worth exploring if we can do something about. > > For a cluster of machines all running with synchronized > clocks. CLOCK_REALTIME matches. CLOCK_MONOTNIC does not match between > machines. Not having a matching CLOCK_MONOTONIC prevents successful > process migration between nodes in that cluster. > > Would it be possible to allow setting CLOCK_MONOTONIC at the very > beginning of time? So that all of the nodes in a cluster can be in > sync? > > No change in skew just in offset for CLOCK_MONOTONIC. > > There are also dragons involved in coordinating things so that > CLOCK_MONOTONIC gets set before CLOCK_MONOTONIC gets used. So I don't > know if allowing CLOCK_MONOTONIC to be set would be practical but it > seems work exploring all on it's own. It's used very early on in the kernel, so that would be a major surprise for many things including user space which has expectations on clock monotonic. It would be reasonably easy to add CLOCK_MONONOTIC_SYNC which can be set in the way you described and then in name spaces make it possible to magically map CLOCK_MONOTONIC to CLOCK_MONOTONIC_SYNC. It still wouldn't allow to have different NTP/PTP time domains, but might be a good start to address the main migration headaches. Thanks, tglx
