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Subject: Re: [OMPI users] openMPI asychronous communication
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2010-06-29 07:07:57


I would advise pre-posting MPI_Irecv's if you know that messages will be coming.

Barriers should only be used if you need to synchronize between groups of processes. Keep in mind that MPI is a lossless/reliable message delivery mechanism, so there's no need for you to call additional error-correcting API functions to ensure that you get all the messages that were sent.

Additionally, Iprobe is typically only useful if you don't know the size / sender of the message. Calling Iprobe almost guarantees that MPI will need to make an internal copy of the message. So avoid probe / iprobe if you can.

On Jun 28, 2010, at 5:16 PM, amjad ali wrote:

> I guess that if the receiver want to ensure that the sender should send data only when the receiver will be able/free to receive data,
>
> then use MPI-Barriers.
>
>
>
> On Mon, Jun 28, 2010 at 12:53 PM, David Zhang <solarbikedz_at_[hidden]> wrote:
> Use MPI_Iprobe. It's a nonblocking probe that allow you to see if a message is coming. So in your receiver code you just periodically probe to see if messages are coming your way.
>
>
> On Sun, Jun 27, 2010 at 9:11 PM, Jack Bryan <dtustudy68_at_[hidden]> wrote:
> thanks
>
> I know that.
>
> MPI_irecv() ;
>
> do other works;
>
> MPI_wait();
>
> But, my message receiver is much slower than sender.
>
> when the sender is doing its local works, the sender has sent out their messages. but at this time,
> the sender is very busy doing its local work and cannot post MPI_irecv to get the messages from
> senders.
>
> Any help is appreciated.
>
> jack
>
>
>
> From: jiangzuoyan_at_[hidden]
> Date: Mon, 28 Jun 2010 11:55:32 +0800
>
> To: users_at_[hidden]
> Subject: Re: [OMPI users] openMPI asychronous communication
>
> OK, then i think you also know using MPI_Wait to wait the asynchronous requests to complete. if sender works faster then receiver(or reverse), then the MPI_Wait will do wait, not just deallocted. you should keep the buffer content before MPI_Wait.
>
> Changsheng Jiang
>
>
> On Mon, Jun 28, 2010 at 11:41, Jack Bryan <dtustudy68_at_[hidden]> wrote:
> thanks
>
> I know this.
>
> but, what if sender can send a lot of messages to receivers faster than what receiver can receive ?
>
> it means that sender works faster than receiver.
>
> Any help is appreciated.
>
> jack
>
>
> From: jiangzuoyan_at_[hidden]
> Date: Mon, 28 Jun 2010 11:31:16 +0800
> To: users_at_[hidden]
> Subject: Re: [OMPI users] openMPI asychronous communication
>
>
> MPI_Isend - Starts a standard-mode, nonblocking send.
>
> BTW, are there any asynchronous collective operations?
>
> Changsheng Jiang
>
>
> On Mon, Jun 28, 2010 at 11:22, Jack Bryan <dtustudy68_at_[hidden]> wrote:
> Dear All:
>
> How to do asychronous communication among nodes by openMPI or boot.MPI in cluster ?
>
> I need to set up a kind of asychronous communication protocol such that
> message senders and receivers can communicate asychronously without losing any
> messages between them.
>
> I do not want to use blocking MPI routines because the processors can do other
> operations when they wait for new messages coming.
>
> I donot find this kind of MPI routines that support this
> asychronous communication.
>
> Any help is appreciated.
>
> thanks
>
> Jack
>
> June 27 2010
>
> The New Busy think 9 to 5 is a cute idea. Combine multiple calendars with Hotmail. Get busy.
>
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>
>
> The New Busy think 9 to 5 is a cute idea. Combine multiple calendars with Hotmail. Get busy.
>
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>
>
> The New Busy think 9 to 5 is a cute idea. Combine multiple calendars with Hotmail. Get busy.
>
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>
>
>
> --
> David Zhang
> University of California, San Diego
>
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-- 
Jeff Squyres
jsquyres_at_[hidden]
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