On Mon, 1 Oct 2018, Andrey Vagin wrote: > On Mon, Oct 01, 2018 at 11:15:32AM +0200, 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? > > Here is a question about how to synchronize clocks between nodes. It > looks like we will need to have a working network for this, but a > network configuration may be non-trivial and it can require to run a few > processes which can use CLOCK_MONOTNIC... > > > > > 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. > > > > Dmitry would setting CLOCK_MONOTONIC exactly once at boot time solve > > your problem that is you are looking at a time namespace to solve? > > Process migration is only one of use-cases. Another use-case is > restoring from snapshots. It may be even more popular than process > migration. We can't guarantee that all snapshots will be done in one > cluster. For example, a user meets a bug, does a container snapshot and > attaches it to a bug report. Sure, but see my reply to Eric. That could be solved with that extra clock id, which then gets mapped to monotonic for name spaces. Thanks, tglx
