Re: [OMPI devel] extracting MPI message tag at the btl level

[George Bosilca]

Karol,






  Thanks,
    george.

On Jul 2, 2007, at 4:56 PM, Karol Mroz wrote:

There is no way to know the MPI tag at the BTL level. The BTL is protocol agnostic, it only moves bytes around (BTL = Byte Transport Layer). Moreover, the BTLs can be (and are) used by different PML, each of them supporting a different protocol. Now, let talk specifically about the OB1 PML. The first X bytes contain a message header, but this message header differ based on the protocol used to transmit the message. There are multiple protocols: eager, send/recv, RDMA. If you look in ompi/mca/pml/ob1/pml_ob1_hdr.h you will see the different types of headers used by the OB1 PML. However, do not use this file in the BTL, as the BTL is PML agnostic.

Good morning everyone. I had a question about obtaining the message tag

from the iovec array in mca_btl_sctp_frag_t* frag from within the

When I extract this, I get a number that resembles an address.
Dereferencing this gives, from what I can tell, an incorrect value and
passing the value into ntohl() etc brings me no closer. There is


Thanks,
Karol

--
Karol Mroz
km...@cs.ubc.ca

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mca_btl_tcp_frag_send() function. If I understand correctly, the first X bytes in the first iovec entry contain message header information in the form of an mca_pml_ob1_match_hdr_t struct that contains a hdr_tag field. probably something basic I'm overlooking... any help would be appreciated.

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