This creates a really bad scaling behavior. Users have found a nearly 20% launch time differential between mpirun and PMI, with PMI being the slower method. Some of the problem is attributable to poor exchange algorithms in RM's like Slurm and Alps, but we make things worse by calling "get" so many times.
Nathan (with a tad advice from me) has attempted to alleviate this problem by reducing the number of "get" calls. This required the following changes:
* upon first request for data, have the OPAL db pmi component fetch and decode *all* the info from a given remote proc. It turned out we weren't caching the info, so we would continually request it and only decode the piece we needed for the immediate request. We now decode all the info and push it into the db hash component for local storage - and then all subsequent retrievals are fulfilled locally
* reduced the amount of data by eliminating the exchange of the OMPI_ARCH value if heterogeneity is not enabled. This was used solely as a check so we would error out if the system wasn't actually homogeneous, which was fine when we thought there was no cost in doing the check. Unfortunately, at large scale and with direct launch, there is a non-zero cost of making this test. We are open to finding a compromise (perhaps turning the test off if requested?), if people feel strongly about performing the test
* reduced the amount of RTE data being automatically fetched, and fetched the rest only upon request. In particular, we no longer immediately fetch the hostname (which is only used for error reporting), but instead get it when needed. Likewise for the RML uri as that info is only required for some (not all) environments. In addition, we no longer fetch the locality unless required, relying instead on the PMI clique info to tell us who is on our local node (if additional info is required, the fetch is performed when a modex_recv is issued).
Again, all this only impacts direct launch - all the info is provided when launched via mpirun as there is no added cost to getting it
Barring objections, we may move this (plus any required other pieces) to the 1.7 branch once it soaks for an appropriate time.
This commit was SVN r29040.
This commit reintroduces key compression into the pmi db. This feature
compresses the keys stored into the component into a small number of
PMI keys by serializing the data and base64 encoding the result. This
will avoid issues with Cray PMI which restricts us to ~ 3 PMI keys per
rank.
This commit was SVN r28993.
Add support for MPI_Count type and MPI_COUNT datatype and add the required
MPI-3 functions MPI_Get_elements_x, MPI_Status_set_elements_x,
MPI_Type_get_extent_x, MPI_Type_get_true_extent_x, and MPI_Type_size_x.
This commit adds only the C bindings. Fortran bindins will be added in
another commit. For now the MPI_Count type is define to have the same size
as MPI_Offset. The type is required to be at least as large as MPI_Offset
and MPI_Aint. The type was initially intended to be a ssize_t (if it was
the same size as a long long) but there were issues compiling romio with
that definition (despite the inclusion of stddef.h).
I updated the datatype engine to use size_t instead of uint32_t to support
large datatypes. This will require some review to make sure that 1) the
changes are beneficial, 2) nothing was broken by the change (I doubt
anything was), and 3) there are no performance regressions due to this
change.
Increase the maximum number of predifined datatypes to support MPI_Count
Put common get_elements code to ompi/datatype/ompi_datatype_get_elements.c
Update MPI_Get_count to reflect changes in MPI-3 (return MPI_UNDEFINED when the count is too large for an int)
This commit was SVN r28932.
This commit adds an API for registering and querying performance
variables (mca_base_pvar) in the MCA base. The existing MCA variable
system API has been updated to reflect the new API: MCA variable
groups have performance variables, and new types have been added (double,
unsigned long long) to reflect what is required by the MPI_T
interface. Additionally, the MCA variable group code has been split
into its own set of files: mca_base_var_group.[ch].
Details of the new API can be found in doxygen comments in the header:
mca_base_pvar.h.
Other changes to the variable system:
- Use an opal_hash_table to speed up variable/group lookup.
- Clean up code associated with MCA variable types.
- Registered performance variables are printed by ompi_info -a. In the
future an option should be added to control this behavior.
Changes to OMPI:
- Added full support for the MPI_T performance variable interface.
This commit was SVN r28800.
(since this is used in the fast path) for when you ''know'' that there
will be a room available:
* Don't do the last_unoccupied_room check
* Return void
This commit was SVN r28757.
Add an option to ompi_info (-l, --level) that takes a number in the
interval (1,9). Only MCA variables up to this level will be printed.
The default level is 1.
Print the level as part of both the parsable and readable output.
This commit was SVN r28750.
sandbox team has informed me that they are getting rid of SANDBOX_PID
in the future and that using SANDBOX_ON would be preferred.
This commit was SVN r28708.
To resolve this situation, add the ability to specify a backend topology file that mpirun shall use for its mapping operations. Create a new "set_topology" function in opal hwloc to support it.
This commit was SVN r28682.
Chose the crc32 function present in opal/util/crc.c as the hash function. The
performance should be sufficient for most cases. If not we can always change
the function again.
This commit was SVN r28629.
