I've been working recently on bumping up the efficiency of MPI data transfer. To date transfer of matrices has been pretty fast, going directly via memory, but bundles have been a lot slower: we took the approach of serializing the bundle to XML at the source end, passing the XML bytes, then deserializing at the destination end. This has been quite reliable (modulo a few bugs that Marcin has brought to light!) but it's inherently clunky. Now in git I've arranged for mpibcast, mpisend and mpirecv to work directly for bundles -- and as a by-product, enabled MPI transfer for arrays. I've done a fair amount of testing of "direct" mpibcast of bundles, and that's currently the default in git. The default for mpisend/mpirecv is still the old XML method (since I just coded the new variant today and it's barely tested) but if you're building gretl yourself you can try out the new variants thus: look for the definition of ALT_BUNSEND in lib/src/gretl_mpi.c and change it from 0 to 1. (I should mention, none of the new stuff is in the Windows or Mac snapshots just yet.) I'll do more testing myself, but if anyone else wants to join in, please do. My results so far are very encouraging. Here's some comparative output from a script that transfers a bundle holding an array of 20 big matrices: old XML-based version: gretlmpi 2019d-git Current session: 2019-10-17 15:00 have 20 matrices bcast time: 1.63798s got 20 matrices send/recv time: 1.59941s diff_arrays gave 8.88178e-16 new direct version: gretlmpi 2019d-git Current session: 2019-10-17 15:01 have 20 matrices bcast time: 0.0132543s got 20 matrices send/recv time: 0.0054283s diff_arrays gave 0 (The non-zero "diff_arrays" value for the XML method is a trivial result of the round-trip serialization and deserialization, but it's nice to see it go to true zero under the direct method.) Here's the script in question: <hansl> set verbose off function scalar diff_arrays (const matrices M1, const matrices M2) scalar maxdiff = 0 loop i=1..nelem(M1) -q scalar d = max(abs(M1[i] - M2[i])) if d > maxdiff maxdiff = d endif endloop return maxdiff end function mpi --send-functions bundle b if $mpirank == 0 matrices b.MM = array(20) loop i=1..nelem(b.MM) -q b.MM[i] = mnormal(1000,100) endloop printf "have %d matrices\n", nelem(b.MM) set stopwatch endif mpibcast(&b) if $mpirank == 0 printf "bcast time: %gs\n", $stopwatch endif set stopwatch if $mpirank == 1 printf "got %d matrices\n", nelem(b.MM) mpisend(b, 0) elif $mpirank == 0 c = mpirecv(1) printf "send/recv time: %gs\n", $stopwatch scalar d = diff_arrays(b.MM, c.MM) printf "diff_arrays gave %g\n", d endif end mpi --np=4 </hansl> Allin