[MPICH2-dev] RE: alignment hints for calculating the file domain.

[Yu, Weikuan]

> -----Original Message-----
> From: Robert Latham [mailto:robl at mcs.anl.gov] 
> 
> On Tue, Jul 10, 2007 at 08:55:18AM -0400, Yu, Weikuan wrote:
> > Wangdi has observed a lot of lock contentions when the file domain 
> > partitions in collective IO are not aligned on Lustre 
> stripe boundary 
> > (say 1MB). As a remedy of that, we are proposing a minor 
> change on the 
> > implementation of ADIOI_GEN_Calc_file_domains() for it to 
> respect an 
> > advisory alignment. The attached patch illustrates what we are 
> > proposing.
> 
> Ok, so you turn fd_size from an output parameter to an in/out 
> parameter.  I don't think that's introducing noticeably more 
> complexity to the interface.  

Right, that's the intention. We want to avoid a new function which adds
very little to the existing one.

> 
> Before you call calc_file_domains, how will you set fd_size?  
> Through a hint the user can override? 

We can do that with a separate ADIO driver. For Lustre, we can find out
the stripe_size from the file attributes. Users can also suggest an hint
on stripe_size of new files. 

--Weikuan

> 
> > P.S.: We will use mpich-discuss at mcs.anl.gov for further 
> discussions if 
> > mpich2-dev is not for this purpose.
> 
> I think this list will be fine.
> 
> ==rob
> 
> --
> Rob Latham
> Mathematics and Computer Science Division    A215 0178 EA2D B059 8CDF
> Argonne National Lab, IL USA                 B29D F333 664A 4280 315B
>