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Subject: Re: [OMPI users] How to checkpoint atomic function in OpenMPI
From: Nguyen Toan (nguyentoan1508_at_[hidden])
Date: 2010-07-22 13:16:06


Dear Josh,
I hope to see this new API soon. Anyway, I will try these critical section
functions in BLCR. Thank you for the support.

Best Regards,
Nguyen Toan

On Sat, Jul 17, 2010 at 6:34 AM, Josh Hursey <jjhursey_at_[hidden]> wrote:

>
> On Jun 14, 2010, at 5:26 AM, Nguyen Toan wrote:
>
> > Hi all,
> > I have a MPI program as follows:
> > -------------------
> > int main(){
> > MPI_Init();
> > ......
> > for (i=0; i<10000; i++) {
> > my_atomic_func();
> > }
> > ...
> > MPI_Finalize();
> > return 0;
> > }
> > --------------------
> >
> > The runtime of this program mainly involves in running the loop and
> my_atomic_func() takes a little bit long.
> > Here I want my_atomic_func() to be operated atomically, but the timing of
> checkpointing (by running ompi-checkpoint command) may be in the middle of
> my_atomic_func() operation and hence ompi-restart may fail to restart
> correctly.
> >
> > So my question is:
> > + At the checkpoint time (executing ompi-checkpoint), is there a way to
> let OpenMPI wait until my_atomic_func() finishes its operation?
>
> We do not currently have an external function to declare a critical section
> during which a checkpoint should not be taken. I filed a ticket to make one
> available. The link is below if you would like to follow its progress:
> https://svn.open-mpi.org/trac/ompi/ticket/2487
>
> I have an MPI Extension interface for C/R that I will be bringing into the
> trunk in the next few weeks. I should be able to extend it to include this
> feature. But I can't promise a deadline, just that I will update the ticket
> when it is available.
>
> In the mean time you might try to use the BLCR interface to define critical
> sections. If you are using the C/R thread then this may work (though I have
> not tried it):
> cr_enter_cs()
> cr_leave_cs()
>
> > + How does ompi-checkpoint operate to checkpoint MPI threads?
>
> We depend on the Checkpoint/Restart Service (e.g., BLCR) to capture the
> whole process image including all threads. So BLCR will capture the state of
> all threads when we take the process checkpoint.
>
> -- Josh
>
> >
> > Regards,
> > Nguyen Toan
> > _______________________________________________
> > users mailing list
> > users_at_[hidden]
> > http://www.open-mpi.org/mailman/listinfo.cgi/users
>
>
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