[mpich-discuss] aggregator in collective I/O

[Rob Latham]

On 10/16/2014 10:07 PM, Jaln wrote:
> Hi,
> How can I know the aggregator's rank in the collective I/O?

fd->hints->ranklist[] contains an array of MPI ranks assigned to an 
aggregator.


> I also feel difficult to distinguish the aggregator and non-aggregator
> in the ad_read_coll.c,
> for example, in function ADIOI_R_Exchange_data,
> how can I know it is executed by a process or an aggregator?
> I can only see how 'nprocs_for_coll' is used in partitioning the file
> domain,
> but couldn't see how it is used to tell the certain number of aggregator
> to do the collective I/O.

I think you want to look at ADIOI_Calc_aggregator, which will report 
which MPI-IO aggregator is responsible for which regions of a file, and 
how much.

ADIOI_R_Exchange_data is called by every process.  Some processes are 
receiving data from an aggregator, and aggregators are sending read 
data, but everyone participates.

Take a look earlier on:  ADIOI_Calc_my_req and ADIOI_Calc_others_req are 
two of the routines responsible for generating the schedule of requests.

==rob

-- 
Rob Latham
Mathematics and Computer Science Division
Argonne National Lab, IL USA
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