[mpich-discuss] messages queue

[Jarosław Bułat]

Hi!

> > I understand this behaviour, what's more, I expected something similar,
> > however I thought the internal buffer is much more bigger or at least it
> > can be enlargement. My application is working with video frames (~1MB).
> > I thought it can be possible to send a few messages (frames) to a queue
> > and receive it at once (sometimes sender is much more faster then
> > receiver which is very busy and is not able to receive all messages in
> > time). 
> > 
> > I assume, that application of non-blocking sending instead of MPI_Send()
> > resolve this problem. Is it true?
> > 
> > Is the internal MPICH2 buffer fixed in size and cannot be enlargement?
> 
> When you're using the sock channel you need to increase the tcp buffers. 
>   To do this you need to do this as root:
> echo 262142 > /proc/sys/net/core/rmem_max
> echo 262142 > /proc/sys/net/core/rmem_default
> 
> In nemesis, set MPID_NEM_NUM_CELLS in
> src/mpid/ch3/channels/nemesis/nemesis/include/mpid_nem_datatypes.h
> Note, however, that cells are 64KB each, so be careful how much you 
> increase this by.
>
>
> As I mentioned, I think a better solution would be to use MPI_Isend() if 
> you can.  With Isend, you won't be using the tcp buffers or 
> shared-memory queues which are a limited resource.  Instead the send 
> queue will be stored in user memory, which is not limited (well, until 
> you run out of memory :-) ).  Of course with Isend, you'll have to make 
> sure you call MPI_Test or MPI_Wait to free the requests and so you know 
> when the send buffer can be reused.

This is exactly what I need. Thank you!


Jarek!