[Lustre-discuss] Shared pointers, file locking and MPI-IO
Sébastien Buisson
sebastien.buisson at bull.net
Thu Oct 23 07:06:33 PDT 2008
Hi all,
We are using MPI-IO on Lustre, so that we can achieve good performance
when writing or reading the same file from multiple processes and clients.
In the shared pointers read/write routines, MPI-IO makes an intensive
use of file locks (for instance, see the file
src/mpi/romio/adio/common/ad_get_sh_fp.c from mpich2-1.0.7). The problem
is that file locking support in Lustre is very limited today:
- there is the localflock option for the local mode. In this mode, locks
are coherent on a node (a single-node flock), but not across all clients;
- there is the flock option for the consistent mode. In this mode, locks
are coherent across all clients. But the Lustre Operations Manual
includes a big warning about this mode, saying that it can affect
performance and stability.
That being said, does anybody in the Lustre community know about current
alternatives to the MPI-IO shared pointers read/write routines, which do
not use the file locking mechanism but provide the same functionality?
By the way, do we have an idea of the Lustre version that will provide
the reliable version of the flock consistent mode?
Best regards,
Sebastien.
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