[CRIU] Question: Tightly coupled applications

[Adrian Reber]

On Sun, Jun 24, 2018 at 02:05:46PM +0100, Thouraya TH wrote:
> 2018-06-23 19:49 GMT+01:00 Thouraya TH <thouraya87 at gmail.com>:
> 
> > 2018-06-23 18:44 GMT+01:00 Adrian Reber <adrian at lisas.de>:
> >
> >> On Sat, Jun 23, 2018 at 02:11:10PM +0100, Thouraya TH wrote:
> >> > *MPI applications would be to be aware of the communication that is
> >> going
> >> > on and try to restore that communication state after the process
> >> restore. *
> >> >
> >> > This is about MPI library https://www.open-mpi.org/
> >> > 1) Running HPC applications, in containers, is gaining significant
> >> interest
> >> > due to lighweight virtualisation of containers versus VMs (as i know).
> >>
> >> Not sure if you are actually asking something here or not. The thing you
> >> need to be concerned about are communication messages which are on the
> >> fly. Especially if the underlying technology is reliable and does not
> >> lose any messages. This can lead to a situation like this
> >> (theoretically):
> >>
> >>  * Side A sends message M1 to side B
> >>  * Side B is checkpointed and stopped before receiving message M1
> >>  * Side A waits for an answer from side B (message M2)
> >>  * Network discards the message M1 as receiver on side B is gone
> >>  * Side B is restored and waits for ever for message M1
> >>
> >>  * Side B keeps now waiting for message M1
> >>  * Side A keeps waiting for message M2
> >>
> >> And now both sides are waiting for ever and you would need to replay
> >> message M1.
> >>
> >> So coordinated checkpointing, where you can make sure that no messages
> >> are currently on the fly, would make it easier.
> >>
> >
> > *Ok, we can use coordinated or uncoordinated checkpointing using CR*IU ?
> >
> OpenMPI
> 
> Status: stalled
> 
>    - Adrian Reber did <https://lisas.de/~adrian/open-mpi.git/> first
>    version of patches
> 
>   I see that this is your version. Is it a coordinated or uncoordinated
> checkpointing ? Kind regards.

Actually I do not remember how and what Open MPI does in regards to
checkpointing. I am guessing it is uncoordinated.

At this point in time, if you want to use CRIU and one of the MPI
variants, you have to implement it yourself.

		Adrian