[Darshan-users] Darshan & EPCC benchio different behaviour

[Piero LANUCARA]

Hi Phil

totally agree.

I really appreciated your support very much.

P.S is it possible to undestand at a more detailed level all the parser 
output?

I still have some problem while trying to relate some of those values. 
For example, running MPIIO version, the following appears:

1) MPIIO_F_WRITE_TIME      103.772865

2)MPIIO_F_MAX_WRITE_TIME  3.107764

3)MPIIO_F_WRITE_START_TIMESTAMP   22.217328

  4) MPIIO_F_CLOSE_START_TIMESTAMP   25.707373

so, is difficult to relate one with two or one with three, four values.

thanks again

Piero

Il 13/02/2020 14:18, Carns, Philip H. ha scritto:
> Thanks Piero.  I agree, but from a practical point of view, I don't 
> see many options for improving Darshan's handling of this particular 
> scenario.  If something in the Fortran runtime is impacting perceived 
> I/O performance, then the only way to observe it would be to 
> wrap/instrument at the Fortran level rather than at the system library 
> (libc) level.  Otherwise Darshan can't tell the difference between the 
> Fortran calls being slow or the Fortran calls being fast with the app 
> doing something else in between calls.
>
> We've been reluctant to pursue that approach (we've hit cases before 
> where instrumenting the Fortran level would have been helpful) because 
> of the development/maintenance cost, in part because there is so much 
> variety in the Fortran compiler world, and in part because our team 
> simply doesn't have a lot of Fortran expertise.
>
> That said, we would entertain a contribution along these lines ��  
> Something like that could be enabled as a compile-time option.
>
> The good news (as you've seen with the MPI tests from benchio) is that 
> what you are describing isn't really a problem for the MPI-IO 
> interface.  Most of the existing MPI-IO Fortran bindings map almost 
> directly to the underlying C MPI-IO bindings, meaning that what we 
> measure at that level should be a pretty accurate indication of what's 
> going on at the Fortran level.  The scenario you have hit is an issue 
> because the Fortran I/O calls likely have more logic that actually 
> resides in the Fortran runtime itself.
>
> thanks,
> -Phil
> ------------------------------------------------------------------------
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