[mpich-discuss] How is MPI Initialization done ?

[Ravi Thati]

Thanks Krishna for ur efforts.
But,
I am expressing this doubt related to *MPICH-G2 means mpich1 device globus2.
*
How  is all-to-all (hostname+port no) exchange is done) ?

As far as now I traced till the calls to
globus_duroc_runtime_inter_subjob_send from the  intra_subjob_send call
which is again called from intra_subjob_bcast call.

Is this globus_duroc_runtime_inter_subjob_send
,globus_duroc_runtime_inter_subjob_receive exchage through the hostname+port
through gatekeeper or any other ports ??

Any help will be great indeed.

On Tue, Mar 11, 2008 at 5:54 PM, Krishna Chaitanya <kris.c1986 at gmail.com>
wrote:

> Hi,
>         I have traced through the point to point module a few times. So,
> may be I can share the flow of events :
> MPI_Init does some basic error checking first and calls MPIR_Init_thread()
> which primarily populates the MPIR_Process data structure, which also
> includes the communicator structure. Apart from that, it also initialises
> some other global variables and the channel interface.
>
> > How the initial communication is established in order to exchange the
> hostname+ port number details ?
>          Suppose, you are using the standard blocking send mode, the bulk
> of this work is done in the MPID_Send() function. Here, the library either
> selects the eager mode or the rendezvous mode ,depending on the size of the
> message that you intend to transfer. There is a cut-off size (
> vc->eager_max_msg_sz )  upto which the library chooses the eager mode, for
> data sizes beyond this, the rendezvous mode is selected.
>          Suppose, the message is small and the data is contiguous,either
> the MPIDI_CH3_EagerContigShortSend() function is invoked. Over here, the
> eager packet is initialized and the data is copied from the buffer to the
> eager packet and invokes the MPIDI_CH3_iStartMsg(). This function examines
> the current connection state, since it is the first call, it is still
> un-connected. It creates the request data structure and enqueues it. The
> progress engine takes care of the request from here. The library now tries
> to form a new connection to the node whose rank has been specified,by
> invoking the MPIDI_CH3I_VC_post_connect() function. The destination is
> already known to the library through the rank and the hostname( mpd.hosts).
> This function gets the info related to the destination IP and the port
> address.
>          The library now invokes the progress engine, through the call to
> MPIDI_CH3i_Progress_wait(). The actual connection establishment and the data
> transfer takes place in this function through the calls to
> MPIDI_CH3I_Progress_handle_sock_event() and MPIDU_Sock_wait(). It loops
> around till the completion counter is set to 1.
>
> >How is the hostname+port number details sent and received
>          I remember Dave had once helped me out with this :
> http://wiki.mcs.anl.gov/mpich2/index.php/Sock_conn_protocol
>
>          Its quite copious in content. The best way to understand what is
> happening is to actually trace through the entire progress engine.
>
> > How is all-to-all communication is done? On which ports this will be
> done ?
>          I am sure the other experienced members would help you on this. I
> havent done much in this area.
>
>          I just have a few months exposure to MPICH. If I have gone wrong
> somewhere, please do correct me.
>
> Best,
> Krishna Chaitanya K,
> Final Year B-Tech,
> Dept. of Information Technology,
> National Institute of Technology,Karnataka (NITK)
>
>
>
>
>
>
> On Tue, Mar 11, 2008 at 3:15 AM, Ravi Thati <gotothati at gmail.com> wrote:
>
> > Hello All,
> >
> >       I am working with MPICH-G2.
> >        I came to know  (from mailing search) that  while MPI_Init is
> > called , the initialization is being done.
> >       All-to-all exchange of host+port details is done.
> >
> > My doubt is :
> >
> >  How the initial communication is established in order to exchange the
> > hostname+ port number details ?
> >  How is the hostname+port number details sent and received ? what are
> > the destination IPs these packets?
> >
> >  How is all-to-all communication is done? On which ports this will be
> > done ?
> >  Only after the exchange , each process can communicate with other.
> >
> >    Thanks for any clarifications.
> > --
> > Regards,
> > Ravi.Thati
>
>
>
>
> --
> In the middle of difficulty, lies opportunity




-- 
Thanks & Regards,
Ravi.Thati
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