Hi, Sorry but I made a mistake... I'm not trying to use PVFS over NFS but PVFS over EXT3. I still don't know this error message...
On Thu, May 29, 2008 at 5:33 PM, Robert Latham <r...@mcs.anl.gov> wrote: > On Thu, May 29, 2008 at 04:48:49PM -0300, Davi Vercillo C. Garcia wrote: >> > Oh, I see you want to use ordered i/o in your application. PVFS >> > doesn't support that mode. However, since you know how much data each >> > process wants to write, a combination of MPI_Scan (to compute each >> > processes offset) and MPI_File_write_at_all (to carry out the >> > collective i/o) will give you the same result with likely better >> > performance (and has the nice side effect of working with pvfs). >> >> I don't understand very well this... what do I need to change in my code ? > > MPI_File_write_ordered has an interesting property (which you probably > know since you use it, but i'll spell it out anyway): writes end up > in the file in rank-order, but are not necessarily carried out in > rank-order. > > Once each process knows the offsets and lengths of the writes the > other process will do, that process can writes its data. Observe that > rank 0 can write immediately. Rank 1 only needs to know how much data > rank 0 will write. and so on. > > Rank N can compute its offset by knowing how much data the proceeding > N-1 processes want to write. The most efficent way to collect this is > to use MPI_Scan and collect a sum of data: > > http://www.mpi-forum.org/docs/mpi-11-html/node84.html#Node84 > > Once you've computed these offsets, MPI_File_write_at_all has enough > information to cary out a collective write of the data. > > ==rob > > -- > Rob Latham > Mathematics and Computer Science Division A215 0178 EA2D B059 8CDF > Argonne National Lab, IL USA B29D F333 664A 4280 315B > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users > -- Davi Vercillo Carneiro Garcia Universidade Federal do Rio de Janeiro Departamento de Ciência da Computação DCC-IM/UFRJ - http://www.dcc.ufrj.br "Good things come to those who... wait." - Debian Project "A computer is like air conditioning: it becomes useless when you open windows." - Linus Torvalds "Há duas coisas infinitas, o universo e a burrice humana. E eu estou em dúvida quanto o primeiro." - Albert Einstein
