Hi all, On Nov 10, 2010, at 11:04 AM, Mark Howison wrote:
> On Wed, Nov 10, 2010 at 11:47 AM, Rob Latham <[email protected]> wrote: >> I see, thanks to jumpshot, that you now have many processors doing >> metadata updates before closing the file. for this small test, 21 out >> of 256 processors (ranks 0-21) do an MPI_FILE_WRITE_AT. Used to all >> come from rank 0. Neat! >> Could that final metadata update be done collectively? I think you've >> explained to me why it could before, but I'm drawing a blank. > > Hi Rob, > > You are probably seeing the "round-robin" metadata writing > optimization that came out of our work tuning HDF5 for Lustre that we > presented at IASDS2010. I'm guessing that you are seeing only 22 > writes because that is how many individual pieces of metadata are in > your file. I'm surprised that you are seeing independent MPI writes, > because I thought it did generate collective calls when we were > testing it. > > Eventually, the metadata writes will be consolidated into larger > contiguous pieces once a newer "pagefile" mechanism for metadata is > developed. The round-robin approach is more of a stop-gap until the > pagefile mechanism is available (at which point the metadata writes > should be large enough to interact much better with parallel file > systems). > > (Quincey should correct me on anything I've gotten wrong here.) Nope, you are correct on all accounts, except that we are still currently doing independent I/O calls. I think the next phase of work was to make the metadata I/O collective. I'm working on the page cache design right now and should have something reasonable in about a month or so. Quincey _______________________________________________ Hdf-forum is for HDF software users discussion. [email protected] http://mail.hdfgroup.org/mailman/listinfo/hdf-forum_hdfgroup.org
