[mpich-discuss] stdin redirection

Filippone, Salvatore Salvatore.Filippone at cranfield.ac.uk
Wed Jun 8 07:50:16 CDT 2016

The key term here is "larg(ish)", which I used in my original email to
mean something larger than the limit I was hitting (64KB) but not
*really* large (in my original case I was using a file of around 300KB).
I naturally moved to normal file I/O;  MPI I/O was not quite called for,
because these were just the control parameters for a series of benchmark
runs, not actual input data (which was read and handled separately).


On Wed, 2016-06-08 at 12:46 +0000, Balaji, Pavan wrote:
> If you want to read large files, you should really use MPI-I/O, not
> stdin.  We support reading from stdin for users who migrate from
> sequential programs to parallel programming, but that's not meant to be
> the real mechanism to read files.  I'm not supportive of trying to
> modify mpich for such use cases.
>   -- Pavan
> > On Jun 5, 2016, at 11:18 AM, Seo, Sangmin <sseo at anl.gov> wrote:
> > 
> > Hello Salvatore,
> > 
> > The current MPICH uses pipe to redirect stdin to processes, but pipe
> has a limited capacity (e.g., 64KB in Linux. Please refer to ​
> http://man7.org/linux/man-pages/man7/pipe.7.html). Therefore, if we
> redirect a file, which is larger than the pipe capacity, to stdin, the
> current MPICH implementation is not handling it properly because write()
> does not succeed to write a large data (> the pipe capacity) to the pipe
> for stdin.
> > 
> > I created a ticket for this issue
> (https://trac.mpich.org/projects/mpich/ticket/2336), but I'd recommend
> you to use file I/O in order to handle a large file instead of using
> stdin redirection.
> > 
> > — Sangmin
> > 
> > 

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