[Darshan-users] Q about darshan-analyzer and ranks

[Shane Snyder]

Hi Caz,

Not silly at all, that is a little confusing :)

In 2.x versions of Darshan, 'multi' would indicate that a given Darshan 
log contained file records that were not opened collectively (across all 
ranks, denoted by rank == -1). 'single' would indicate that a log 
contained file records that were opened collectively across all ranks. I 
*think* the thought process for naming that way is that files which are 
accessed by all ranks have a *single* record, whereas applications which 
open independent files on each process have *multiple* file records.

At any rate, in newer versions of Darshan (>=3.0.0), the wording has 
been changed to be more clear. We use 'shared' to denote applications 
which used a single, shared file for I/O (i.e., single=>shared) and we 
use 'fpp' (file-per-process) to indicate logs which have files that were 
opened independently by a certain process (i.e., multi=>fpp).

Also, note that a given log file can be viewed as both single/shared and 
multi/fpp by darshan-analyzer. Any log that has a shared file record in 
it will be classified as single/shared and similarly any log with a file 
that was accessed by either a single rank or a subset of ranks will be 
classified as multi/fpp. The tool is just meant to give a general 
overview of the type of access patterns a directory of logs used.

--Shane

On 07/08/2016 11:47 AM, Casmira, Jason P wrote:
>
> Hello.
>
> Hopefully this isn’t too silly of a question.
>
> I see this code in darshan-analyzer.c:
>
>         if (cp_file.rank == -1)
>
>             *used_single = 1;
>
>         else
>
>             *used_multi = 1;
>
> But from darshan_parser.c:
>
>         printf("\n# description of columns:\n");
>
>         printf("#   <rank>: MPI rank.  -1 indicates that the file is 
> shared\n");
>
>         printf("#      across all processes and statistics are 
> aggregated.\n");
>
> It’s not clear to me how to interpret darshan_analyzer’s use of the 
> rank field.
>
> Intuitively I’m thinking it would be the opposite (-1 == shared == 
> multi), so I think
>
> I’m missing something fundamental here, and I hope someone can clarify 
> for me.
>
> I tried searching on “rank” and “darshan-analyzer” but couldn’t find 
> an answer.
>
> Thanks.
>
> Caz.
>
> Jason Casmira
>
> Intel Corporation
>
> 503.712.5610
>
>
>
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> Darshan-users at lists.mcs.anl.gov
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