On Feb 24, 2009, at 18:08 , Eugene Loh wrote:
(Probably this message only for George, but I'll toss it out to the
alias/archive.)
I have a question about the sm sendi() function. What should happen
if the sendi() function attempts to write to the FIFO, but the FIFO
is full?
The write should not be queued except in the case where the whole data
referred by the convertor is copied out of the user memory. If the
FIFO is full, the best will be to allocate the descriptor and give it
back to the PML.
Currently, it appears that the sendi() function returns an error
code to the PML, which assumes that the sendi() tried to send the
message but failed and so just tried to allocate a descriptor.
Yes, this is the expected behavior.
But is that what should happen? The condition of the FIFO being
full is a little misleading since the write is still queued for
further progress -- not in the FIFO itself but in the pending-send
queue. This distinction should perhaps not matter to the upper
layers. The upper layers should still view the send as
"completed" (buffered by the MPI implementation to be progressed
later). I would think that the sendi() function should return a
SUCCESS code.
If the write is queued then this is more or less a bug. We will nicely
cope with this case, because we have this sequence number and we will
drop a message duplicate, but we will end-up sending the same message
twice. The problem is that I don't know which of the copies will be
used on the receiver side, I guess the first one reaching the receiver.
george.
Relevent source code is
PML, line 496
https://svn.open-mpi.org/source/xref/ompi_1.3/ompi/mca/pml/ob1/pml_ob1_sendreq.c
#496
BTL, line 785
https://svn.open-mpi.org/source/xref/ompi_1.3/ompi/mca/btl/sm/
btl_sm.c#785
FIFO write, line 18
https://svn.open-mpi.org/opengrok/xref/ompi_1.3/ompi/mca/btl/sm/btl_sm_fifo.h
#18
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