possible bug in prerelease

[Wei-keng Liao]

Hi, Jim

I will create a new error code, named NC_EMAX_REQ, in PnetCDF.
So, if the request size of an individual call to a get/put API or
wait API is > 2GiB, then NC_EMAX_REQ will be thrown. Note the
new size limit is per MPI process, not across all MPI processes.
I guess this behavior will affect PIO. Feedbacks are welcomed.

Wei-keng

On Dec 4, 2017, at 10:10 AM, Jim Edwards wrote:

> Yes I can confirm that the aggregated size exceeds 2GiB. 
> 
> On Sun, Dec 3, 2017 at 3:35 PM, Wei-keng Liao <wkliao at eecs.northwestern.edu> wrote:
> Hi, Jim
> 
> I think the error you encountered is most likely due to the
> aggregated size of nonblocking requests in the ncmpi_wait_all
> call being larger then 2 GiB. Can you confirm this is your case?
> ROMIO does not appear to work well for such cases. I am
> thinking to make PnetCDF to bail out if this condition is
> detected.
> 
> Wei-keng
> 
> On Dec 3, 2017, at 7:55 AM, Jim Edwards wrote:
> 
> > I see you already put up the PR to ROMIO - thanks.
> >
> > On Fri, Dec 1, 2017 at 10:52 PM, Wei-keng Liao <wkliao at eecs.northwestern.edu> wrote:
> > Hi, Jim
> >
> > After taking another look at your assertion error from ad_gpfs_aggrs.c,
> > I believe you were hit by a ROMIO bug. I wrote a short test program that
> > can cause a similar integer overflow error in ROMIO. The program's URL:
> > https://trac.mcs.anl.gov/projects/parallel-netcdf/browser/trunk/test/largefile/large_coalesce.c
> >
> > Look like the bug has been predicted based on the following comments at line 463
> > in file ad_gpfs_aggrs.c:
> >   /* Possibly reconsider if buf_idx's are ok as int's, or should they be aints/offsets?
> >      They are used as memory buffer indices so it seems like the 2G limit is in effect */
> >
> > After I rebuilt MPICH by changing the data type of buf_idx from int to MPI_Aint,
> > my test program ran fine. Would you like to create an github issue at MPICH repo?
> >
> >
> > Wei-keng
> >
> > On Dec 1, 2017, at 8:07 PM, Wei-keng Liao wrote:
> >
> > > Hi, Jim,
> > >
> > > Yes, that is a bug. I have developed a fix. Please check out the
> > > latest commit from PnetCDF SVN repo and let me know if it works for you.
> > > Thanks for reporting.
> > >
> > > Wei-keng
> > >
> > > On Dec 1, 2017, at 4:43 PM, Jim Edwards wrote:
> > >
> > >> I think that I've found a bug in the prerelease in file ncmpio_wait.c
> > >>
> > >> In coalescing blocklengths at line 2095
> > >> ​
> > >>            if (ai - a_last_contig == blocklengths[last_contig_req])
> > >>                /* user buffer of request j is contiguous from j-1
> > >>                 * we coalesce j to j-1 */
> > >>                blocklengths[last_contig_req] += blocklengths[j];
> > >>
> > >> ​It's possible that ​blocklengths[last_contig_req] + blocklengths[j]; overflows the integer datatype.
> > >> I tried to fix that by avoiding the coalescing:
> > >>
> > >>            if ((ai - a_last_contig == blocklengths[last_contig_req]) &&
> > >>              (blocklengths[last_contig_req] + blocklengths[j] > 0))
> > >>                /* user buffer of request j is contiguous from j-1
> > >>                 * we coalesce j to j-1 */
> > >>                blocklengths[last_contig_req] += blocklengths[j];
> > >>
> > >> ​but that leads to another overflow problem ​:
> > >> ad_gpfs_aggrs.c:572: ADIOI_GPFS_Calc_my_req: Assertion `curr_idx == (int) curr_idx' failed.
> > >>
> > >>
> > >>
> > >> --
> > >> Jim Edwards
> > >>
> > >> CESM Software Engineer
> > >> National Center for Atmospheric Research
> > >> Boulder, CO
> > >
> >
> >
> >
> >
> > --
> > Jim Edwards
> >
> > CESM Software Engineer
> > National Center for Atmospheric Research
> > Boulder, CO
> 
> 
> 
> 
> -- 
> Jim Edwards
> 
> CESM Software Engineer
> National Center for Atmospheric Research
> Boulder, CO