[mpich-discuss] COMM_SELF and collective IO

[Rajeev Thakur]

COMM_SELF means all=1. So MPI_File_read_all is equivalent to
MPI_File_read in that case.

> -----Original Message-----
> From: mpich-discuss-bounces at mcs.anl.gov 
> [mailto:mpich-discuss-bounces at mcs.anl.gov] On Behalf Of burlen
> Sent: Friday, October 16, 2009 11:56 PM
> To: mpich-discuss at mcs.anl.gov
> Subject: Re: [mpich-discuss] COMM_SELF and collective IO
> 
> Actually, not quite. But if we can put that aside for the 
> moment. Is there a significant downside to using COMM_SELF + 
> MPI_File_read_all compared to just MPI_File_read?
> 
> Rajeev Thakur wrote:
> > You will have the same if you use COMM_SELF for one and 
> COMM_WORLD for 
> > the other. You don't want to use COMM_SELF for both.
> >
> >   
> >> -----Original Message-----
> >> From: mpich-discuss-bounces at mcs.anl.gov 
> >> [mailto:mpich-discuss-bounces at mcs.anl.gov] On Behalf Of burlen
> >> Sent: Friday, October 16, 2009 7:22 PM
> >> To: mpich-discuss at mcs.anl.gov
> >> Subject: Re: [mpich-discuss] COMM_SELF and collective IO
> >>
> >> I could then I will have to have two codes with only a one line 
> >> difference.
> >>
> >> Rajeev Thakur wrote:
> >>     
> >>> Why don't you just use MPI_File_read instead?
> >>>
> >>> Rajeev
> >>>
> >>>   
> >>>       
> >>>> -----Original Message-----
> >>>> From: mpich-discuss-bounces at mcs.anl.gov 
> >>>> [mailto:mpich-discuss-bounces at mcs.anl.gov] On Behalf Of burlen
> >>>> Sent: Friday, October 16, 2009 5:39 PM
> >>>> To: mpich-discuss at mcs.anl.gov
> >>>> Subject: [mpich-discuss] COMM_SELF and collective IO
> >>>>
> >>>> I have an io code that uses the subarray type. I use the
> >>>>         
> >> collective
> >>     
> >>>> IO function, MPI_File_read_all. Now, I have a use case 
> where each 
> >>>> process needs to read independently of the others. What I
> >>>>         
> >> am tempted
> >>     
> >>>> to do is change the communicator to MPI_COMM_SELF and 
> use the same 
> >>>> code. I suspect that this is a bad idea. Is it?
> >>>>
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