coll/base: add support for component name in output

[edgargabriel]

add the ability to output which component provides which collective operation. The feature is controlled by the mca_coll_base_verbose variable. Specifically

mca_coll_base_verbose > 0 and < 20:

• output will be provided for MPI_COMM_WORLD only, and only for the blocking and non-blocking collectives

mca_coll_base_verbose = 20:

• output will be provided for all communicators, but only for blocking and non-blocking collectives

mca_coll_base_verbose > 20:

• output will be provided for all communicators and all collectives (including persistent and ft)

Note that the values are up for negotiation. I am also open to use an entirely new mca parameter that would allow for more natural specification of which communicator/operation we want the output for.

The output looks as follows (small sample):

coll:base:comm_select: communicator MPI_COMM_WORLD rank 0 alltoallv -> tuned
coll:base:comm_select: communicator MPI_COMM_WORLD rank 0 alltoallw -> basic
coll:base:comm_select: communicator MPI_COMM_WORLD rank 0 barrier -> tuned
coll:base:comm_select: communicator MPI_COMM_WORLD rank 0 bcast -> tuned
coll:base:comm_select: communicator MPI_COMM_WORLD rank 0 exscan -> accelerator
coll:base:comm_select: communicator MPI_COMM_WORLD rank 0 gather -> tuned
coll:base:comm_select: communicator MPI_COMM_WORLD rank 0 gatherv -> basic
coll:base:comm_select: communicator MPI_COMM_WORLD rank 0 reduce -> accelerator
coll:base:comm_select: communicator MPI_COMM_WORLD rank 0 reduce_scatter -> tuned
coll:base:comm_select: communicator MPI_COMM_WORLD rank 0 scan -> accelerator
coll:base:comm_select: communicator MPI_COMM_WORLD rank 0 scatter -> tuned
coll:base:comm_select: communicator MPI_COMM_WORLD rank 0 scatterv -> basic
coll:base:comm_select: communicator MPI_COMM_WORLD rank 0 neighbor_allgather -> basic
coll:base:comm_select: communicator MPI_COMM_WORLD rank 0 reduce_local -> basic
coll:base:comm_select: communicator MPI_COMM_WORLD rank 0 iallgather -> libnbc
coll:base:comm_select: communicator MPI_COMM_WORLD rank 0 iallgatherv -> libnbc
...

[edgargabriel]

@bosilca convinced me that the hash-table is not required :-), so second attempt does not use internally a hash-table for mapping module pointers to component names. Thank you !

[bosilca]

Looks good to me.

We should mention that this is only printing the highest priority module for each collective, which in some cases might not be the one executing the collective, when for whatever reason it uses the fallback mechanism to delegate the collective to another module. Unfortunately, there is no way to track that down, so this is really the best we can do right now.