+1
I do not know what you meant by "MPI_Bcast() supports unsigned long long
while MPI_Allgatherv()"
counts (and displacements for MPI_Allgatherv()) are all int according to
the MPI standard.
(and as suggested by Jeff, use BigMPI in order to use MPI_Count instead
of int)
if you mentioned the datatype, both work fine with MPI_INT and
MPI_UNSIGNED_LONG_LONG.
note if your counts are a multiple of a large number, you can create a
vector type, and hopefully the number of vectors you have to transmit
will fit into an int, so you can use standard MPI calls.
Cheers,
Gilles
On 11/29/2017 11:20 AM, Jeff Hammond wrote:
You may be looking for BigMPI (
https://github.com/jeffhammond/BigMPI). The README and paper linked
therein will tell you everything you need to know.
However, BigMPI solves a correctness problem, not a performance one.
If you want to get the faster collectives for multi-gigabyte buffers,
you should roll your own pipelined implementation.
Jeff
On Tue, Nov 28, 2017 at 4:05 PM Konstantinos Konstantinidis
<kostas1...@gmail.com <mailto:kostas1...@gmail.com>> wrote:
Hi, I have a communicator, say /comm/, and some shuffling of data
takes place within its nodes.
I have implemented the shuffling with broadcasts but now I am
trying to experiment with MPI_Allgather() and MPI_Allgatherv().
For demonstration purposes I am adding here a small part of the
C++ code. You can assume that /no_keys/ keys each of size /keysize
/unsigned char//are locally stored at some structure named
/endata, /at each node.
*unsigned keysize = 100;*
*unsigned long long no_keys = 10;*
**
*// unsigned long long bytes_send_count = no_keys*keysize; *
*int bytes_send_count = (int)no_keys*keysize; *
*
*
*unsigned int commSize = (unsigned)comm.Get_size();*
*
*
*// unsigned long long* recv_counts = new unsigned long
long[commSize];*
*int* recv_counts = new int[commSize];*
**
*// unsigned long long* displs = new unsigned long long[commSize];*
*int* displs = new int[commSize]; *
**
*//Εxchange amount of data*
*// comm.Allgather(&bytes_send_count, 1, MPI::UNSIGNED_LONG_LONG,
recv_counts, 1, MPI::UNSIGNED_LONG_LONG); *
*comm.Allgather(&bytes_send_count, 1, MPI::INT, recv_counts, 1,
MPI::INT); *
*
*
*unsigned long long total = 0; *
*for(unsigned int i = 0; i < commSize; i++){*
*displs[i] = total; *
*total += recv_counts[i]; *
*}*
*
*
*unsigned char* recv_buf = new unsigned char[total];*
**
*//Exchange actual data*
*comm.Allgatherv(&endata, no_keys*keysize, MPI::UNSIGNED_CHAR,
recv_buf, recv_counts, displs, MPI::UNSIGNED_CHAR);*
*
*
My problem is that the number of keys is actually big and cannot
fit into an *int*, that's why it is defined as an *unsigned long
long*. So, what I would like to do is basically the commented
lines of code but I get the error that there is no match to this
function if I use *unsigned long long*. Is this true, and if yes
why is that? I don't understand why Bcast() supports unsigned long
long while Allgatherv() does not.
I would like to avoid setting up multiple Allgatherv() calls for
this since the number of connections that are initiated based on
my algorithm is quite big and I am afraid that this will create
further delays. Actually, this is the reason I am trying to
replace Bcast() and try other things.
I am using Open MPI 2.1.2 and testing on a single computer with 7
MPI processes. The ompi_info is the attached file.
_______________________________________________
users mailing list
users@lists.open-mpi.org <mailto:users@lists.open-mpi.org>
https://lists.open-mpi.org/mailman/listinfo/users
--
Jeff Hammond
jeff.scie...@gmail.com <mailto:jeff.scie...@gmail.com>
http://jeffhammond.github.io/
_______________________________________________
users mailing list
users@lists.open-mpi.org
https://lists.open-mpi.org/mailman/listinfo/users
_______________________________________________
users mailing list
users@lists.open-mpi.org
https://lists.open-mpi.org/mailman/listinfo/users
