[mpich-discuss] How to implement this case

Mon Jan 3 15:24:47 CST 2011

Hi Eric,

You are right. An extra MPI_Irecv will be executed at end. Thanks for your
comment.

cheers
Xiao

On Mon, Jan 3, 2011 at 4:16 PM, Eric A. Borisch <eborisch at ieee.org> wrote:

> Looks about right... I'm assuming there is a <do actual work here> to be
> inserted between the MPI_Waitany and MPI_Irecv within the N*M-sized loop....
> and I count from 0 rather than 1 by force of habit... :)
>
> I think the logic below will end with one extra attempted MPI_Irecv than
> desired; perhaps change
>
> if trunk_sent[index] != M do
>    MPI_Irecv(buffer[index], index, requests[index])
>    trunk_sent[index]++
> end
>
> to
>
> if ++trunk_sent[index] != M do
>    MPI_Irecv(buffer[index], index, requests[index])
> end
>
>  -Eric
>
>
> On Mon, Jan 3, 2011 at 3:00 PM, Xiao Li <shinelee.thewise at gmail.com>wrote:
>
>> Hi Eric,
>>
>> Thanks for your detailed suggestion. After read MPI documents, I propose
>> the following algorithm,
>>
>> //begin collecting data for the first trunk
>> for i=1 to N do
>>     MPI_Irecv(buffer[i], i, requests[i])
>> end
>> //set data sending counter
>> for i=1 to N do
>>     trunk_sent[i] = 0
>> end
>> //begin collecting data
>> for i=1 to N*M do
>>     MPI_Waitany(N, requests, &index, &status)
>>     if trunk_sent[index] != M do
>>          MPI_Irecv(buffer[index], index, requests[index])
>>          trunk_sent[index]++
>>     end
>> end
>>
>> May I know what is your opinion of this algorithm?
>>
>> cheers
>> Xiao
>>
>>
>> On Mon, Jan 3, 2011 at 3:31 PM, Eric A. Borisch <eborisch at ieee.org>wrote:
>>
>>> Xiao,
>>>
>>> You should be able to get by with just N buffers, one for each client.
>>> After you have processed the i-th iteration for client n, re-issue an
>>> MPI_Irecv with the same buffer. This will match up with the next MPI_Send
>>> from client n. You don't have to worry about synchronizing -- the MPI_Irecv
>>> does not need to be posted before the MPI_Send. (But the MPI_Send won't
>>> complete until it has been, of course...)
>>>
>>> You could always roll your own sockets, but MPI does a nice job of
>>> managing connections and messages for you. In addition, MPI can be used
>>> fairly efficiently on a wide range of interconnects, from shared memory to
>>> Infiniband with little to no change on the user's part.
>>>
>>> In addition, you could likely improve performance in MPI by having two
>>> sets (call them A and B) of buffers to send from on each worker; one is in
>>> the "send" state (let's call this one A, started with an MPI_Isend after it
>>> was initially filled) while you're filling B. After B is filled, initiate a
>>> new MPI_Isend (very quick) on B and then wait for A's first send (MPI_Wait)
>>> to complete. Once the first send on A is completed, you can start populating
>>> A with the next iteration's output, initiate A's send, wait for B's send to
>>> complete, and the cycle begins again.
>>>
>>> This approach allows you to overlay communication and computation times,
>>> and still works with the MPI_Waitany() approach to harvesting completed jobs
>>> in first-completed order on the master. This is an almost trivial thing to
>>> implement in MPI, but achieving it with sockets requires (IMHO) much more
>>> programmer overhead...
>>>
>>> Just my 2c.
>>>
>>>  Eric
>>>
>>>
>>> On Mon, Jan 3, 2011 at 1:24 PM, Xiao Li <shinelee.thewise at gmail.com>wrote:
>>>
>>>> Hi Eric,
>>>>
>>>> Assume I have N workers and M trunks of sending data for each worker
>>>> respectively, then I have to create N*M data buffer for MPI_Irecv usage. Is
>>>> this method too costly?
>>>>
>>>> Or If I write raw socket programming, is that better? Just like
>>>> traditional client/server socket programming? Master listens on port
>>>> and spawn a new thread to accept worker's data storage request?
>>>>
>>>> cheers
>>>> Xiao
>>>>
>>>>
>>>> On Mon, Jan 3, 2011 at 2:13 PM, Eric A. Borisch <eborisch at ieee.org>wrote:
>>>>
>>>>> Look at the documentation for MPI_Irecv and MPI_Testany ... these
>>>>> should help you do what you want.
>>>>>
>>>>>  Eric
>>>>>
>>>>> On Mon, Jan 3, 2011 at 12:45 PM, Xiao Li <shinelee.thewise at gmail.com>wrote:
>>>>>
>>>>>> Hi MPICH2 people,
>>>>>>
>>>>>> Now, I have a application that composed of single master and many
>>>>>> workers. The application requirement is very simple: workers finish some
>>>>>> jobs and send data to master and master store these data into files
>>>>>> separately. I can simply use MPI_Send on worker side to send data to master.
>>>>>> But master does not know the data sending sequence. Some worker go fast
>>>>>> while some are slow. More specifically, suppose there are 5 workers, then
>>>>>> the data send sequence may be 1,3,4,5,2 or 2,5,4,1,3. If I just write a for
>>>>>> loop for(i=1 to 5) on master side with MPI_Recv to get data, the master and
>>>>>> some faster worker have to wait for a long time. I know MPI_Gather can
>>>>>> implement this. But I am not sure is MPI_Gather works parallelly or just a
>>>>>> sequential MPI_Recv? Another issue is my data is extremely large, more than
>>>>>> 1GB data needed to be sent to master. If I divide the data into pieces, I do
>>>>>> not think MPI_Gather can work. I also tried to think about raw socket
>>>>>> programming, but I do not think it is a good practice. Would you give me
>>>>>> some suggestion please?
>>>>>>
>>>>>> cheers
>>>>>> Xiao
>>>>>>
>>>>>> _______________________________________________
>>>>>> mpich-discuss mailing list
>>>>>> mpich-discuss at mcs.anl.gov
>>>>>> https://lists.mcs.anl.gov/mailman/listinfo/mpich-discuss
>>>>>>
>>>>>>
>>>>> _______________________________________________
>>>>> mpich-discuss mailing list
>>>>> mpich-discuss at mcs.anl.gov
>>>>> https://lists.mcs.anl.gov/mailman/listinfo/mpich-discuss
>>>>>
>>>>>
>>>>
>>>> _______________________________________________
>>>> mpich-discuss mailing list
>>>> mpich-discuss at mcs.anl.gov
>>>> https://lists.mcs.anl.gov/mailman/listinfo/mpich-discuss
>>>>
>>>>
>>> _______________________________________________
>>> mpich-discuss mailing list
>>> mpich-discuss at mcs.anl.gov
>>> https://lists.mcs.anl.gov/mailman/listinfo/mpich-discuss
>>>
>>>
>>
>> _______________________________________________
>> mpich-discuss mailing list
>> mpich-discuss at mcs.anl.gov
>> https://lists.mcs.anl.gov/mailman/listinfo/mpich-discuss
>>
>>
>
> _______________________________________________
> mpich-discuss mailing list
> mpich-discuss at mcs.anl.gov
> https://lists.mcs.anl.gov/mailman/listinfo/mpich-discuss
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/mpich-discuss/attachments/20110103/354e182b/attachment.htm>