[MPICH] slow IOR when using fileview

[Rajeev Thakur]

Can you see what happens if you use type_indexed instead of type_subarray? 

Rajeev

> -----Original Message-----
> From: owner-mpich-discuss at mcs.anl.gov 
> [mailto:owner-mpich-discuss at mcs.anl.gov] On Behalf Of Wei-keng Liao
> Sent: Saturday, June 30, 2007 2:03 AM
> To: mpich-discuss at mcs.anl.gov
> Subject: [MPICH] slow IOR when using fileview
> 
> 
> I am experiencing slow IOR performance on Cray XT3 when using 
> fileview 
> option. I extract the code into a simpler version (attached). 
> The code 
> compares two collective writes: MPI_File_write_all and 
> MPI_File_write_at_all. The former uses an MPI fileview and 
> the latter uses 
> explicit file offset. For both cases, each process writes 10 MB to a 
> shared file, contiguously, non-overlapping, non-interleaved. 
> On the Cray 
> XT3 with Lustre file system, the former is extremely slower than the 
> latter. Here is an output for using 8 processes:
> 
> 2: MPI_File_write_all() time = 4.72 sec
> 3: MPI_File_write_all() time = 4.74 sec
> 6: MPI_File_write_all() time = 4.77 sec
> 1: MPI_File_write_all() time = 4.79 sec
> 7: MPI_File_write_all() time = 4.81 sec
> 0: MPI_File_write_all() time = 4.83 sec
> 5: MPI_File_write_all() time = 4.85 sec
> 4: MPI_File_write_all() time = 4.89 sec
> 2: MPI_File_write_at_all() time = 0.02 sec
> 1: MPI_File_write_at_all() time = 0.02 sec
> 3: MPI_File_write_at_all() time = 0.02 sec
> 0: MPI_File_write_at_all() time = 0.02 sec
> 6: MPI_File_write_at_all() time = 0.02 sec
> 4: MPI_File_write_at_all() time = 0.02 sec
> 7: MPI_File_write_at_all() time = 0.02 sec
> 5: MPI_File_write_at_all() time = 0.02 sec
> 
> I tried the same code on other machines and different file 
> systems (eg. 
> PVFS), and timings for both cases were very close to each 
> other. If anyone 
> has access to a Cray XT3 machine, could you please try it and 
> let me know? 
> Thanks.
> 
> Wei-keng
>