Tomorrow I will add some printf to collective code and check what really
happens there...
Pasha
Peter Kjellstrom wrote:
On Wednesday 20 May 2009, Pavel Shamis (Pasha) wrote:
Disabling basic_linear seems like a good idea but your config file sets
the cut-off at 128 Bytes for 64-ranks (the field you set to 8192 seems to
result in a message size of that value divided by the number of ranks).
In my testing bruck seems to win clearly (at least for 64 ranks on my IB)
up to 2048. Hence, the following line may be better:
131072 2 0 0 # switch to pair wise for size 128K/nranks
Disclaimer: I guess this could differ quite a bit for nranks!=64 and
different btls.
Sounds strange for me. From the code is looks that we take the threshold as
is without dividing by number of ranks.
Interesting, I may have had to little or too much coffe but the figures in my
previous e-mail (3rd run, bruckto2k_pair) was run with the above line. And it
very much looks like it switched at 128K/64=2K, not at 128K (which would have
been above my largest size of 3000 and as such equiv. to all_bruck).
I also ran tests with:
8192 2 0 0 # ...
And it seemed to switch between 10 Bytes and 500 Bytes (most likely then at
8192/64=128).
My testprogram calls MPI_Alltoall like this:
time1 = MPI_Wtime();
for (i = 0; i < repetitions; i++) {
MPI_Alltoall(sbuf, message_size, MPI_CHAR,
rbuf, message_size, MPI_CHAR, MPI_COMM_WORLD);
}
time2 = MPI_Wtime();
/Peter
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