[Lustre-discuss] mpi-io support

[Tom.Wang]

Hi,

Andreas Dilger wrote:
> On May 09, 2008  09:41 -0400, Phil Dickens wrote:
>   
>>   I am having similar struggles with locking on MPI-IO.
>> I am doing a simple strided write, and it fails because
>> of the locking. I'm a bit behind in the discussion, but
>> is there a way to fix (workaround) this problem?? Is this
>> something in my code, or the default driver (this is on
>> lonestar at TACC)? I have even downloaded the most up to date
>> version of MPICH, which I believe has a new Lustre ADIO
>> driver, but I am running into the same issues.
>>
>>   Any thoughts would be greatly appreciated!!
>>     
> One possibility is to mount the clients with "-o localflock", leaving all
> of the locking internal to Lustre.  This in essence provides single-node
> flock (i.e. coherent on that node, but not across all clients).  The other
> alternative is "-o flock", which is coherent locking across all clients,
> but has a noticable performance impact and may affect stability, depending
> on the version of lustre being used (newer is better of course).
>
> I'm not positive of the internals of the MPI-IO code, whether it depends
> on flock providing a barrier across nodes, or if it does this only for
> e.g. NFS not keeping writes coherent so they don't clobber the same page
> when writing.
>
> Tom is the expert here...
>   
It uses flock to keep the coherence of read-modify-write for data_sieving.

You can use

 ierr = MPI_Info_create(&FILE_INFO_TEMPLATE);

 .............
 ierr = MPI_Info_set(FILE_INFO_TEMPLATE, "romio_ds_write", disable);

 to disable data_sieving in your application to avoid flock for 
stride_write.

Thanks
WangDi
>   
>
>   


-- 
Regards,
Tom Wangdi    
--
Sun Lustre Group
System Software Engineer 
http://www.sun.com