Thanks for the feed-back everyone! Actually, even on a serial run I have output writing accounting for 11% of the computational time on Norne. Splitting it in a separate thread with asynchronous writing should bring that down to practically zero with no extra dependencies required, and without memory duplication. Making the writing fully parallel seems like a larger undertaking which can be done for the mpi version.
Cheers, Alf ________________________________________ From: Opm [[email protected]] on behalf of Markus Blatt [[email protected]] Sent: Tuesday, March 15, 2016 11:20 AM To: [email protected] Subject: Re: [Opm] New opm-repo Hi, On Tue, Mar 15, 2016 at 08:47:52AM +0000, Alf Birger Rustad wrote: > Thanks for the announcement! There is one issue that I hope > everybody with informed opinions can contribute to. Today, writing > results is a performance bottleneck flow. Hence, we should find a > way for flow to write results asynchronously, i.e., the simulator > should not need to wait computing the next timestep while the > results are written. It has been suggested to split out the writing > in a separate process to accomplish this, but I am not sure how this > could be done in a good way. Implementing the writer as a server > seems like over-engineering, and we probably do not want to mandate > MPI to run the simulator. The simplest option I can think of is > splitting the writing to a new thread with openmp. As I am the one who brought this up, I have to relativate this a bit. I experienced this bottleneck for a parallel run with 8 cores. The time spent for output was 31% of the total time. For a sequential run it is probably below 10% but I have not measured it. Minimizing the time for the ouput of a sequential run as proposed comes at cost, too. We need to duplicate the memory. What I am concerned about is that the output is not parallel at all which will bite us more when using more cores. Having a dedicated output core is just a first step. Ultimately, we need several cores doing output in parallel in a parallel file format. But this can wait some time, I guess. Cheers, Markus -- Dr. Markus Blatt - HPC-Simulation-Software & Services http://www.dr-blatt.de Hans-Bunte-Str. 8-10, 69123 Heidelberg, Germany, USt-Id: DE279960836 Tel.: +49 (0) 160 97590858 ------------------------------------------------------------------- The information contained in this message may be CONFIDENTIAL and is intended for the addressee only. Any unauthorised use, dissemination of the information or copying of this message is prohibited. If you are not the addressee, please notify the sender immediately by return e-mail and delete this message. Thank you _______________________________________________ Opm mailing list [email protected] http://opm-project.org/cgi-bin/mailman/listinfo/opm
