Thanks for the comment. Another issue I have after thinking about the interface more.
Rank A is the sender, rank B and C are two ranks on a remote node. At first, B creates the receiving QP and make connection to A and register the QP number for receiving. And A gets the receiving QP nubmer from B. After some communication between A and B, B decides to close the connection, and unregister the QP number. Then A and C want to talk, so A tell C the receiving QP number, C tries to register the QP number. I wonder at the time when C tries to register the QP number, the receiving QP has been destroyed by the kernel, since when B unregister the QP number, the reference count becomes zero, and kernel will cleanup it. Am I right ? --CQ > -----Original Message----- > From: Ishai Rabinovitz [mailto:[EMAIL PROTECTED] > Sent: Thursday, January 03, 2008 2:59 AM > To: [EMAIL PROTECTED]; Tang, Changqing; Jack > Morgenstein; Pavel Shamis > Cc: Gleb Natapov; Roland Dreier; [email protected] > Subject: RE: [ofa-general] [RFC] XRC -- make receiving XRC QP > independent of any one user process > > Please see my comments (prefix [Ishai]) > > -----Original Message----- > From: Tang, Changqing [mailto:[EMAIL PROTECTED] > Sent: ד 02 ינואר 2008 17:27 > To: Jack Morgenstein; Pavel Shamis > Cc: Ishai Rabinovitz; Gleb Natapov; Roland Dreier; > [email protected] > Subject: RE: [ofa-general] [RFC] XRC -- make receiving XRC QP > independent of any one user process > > > This interface is OK for me. > > Now, every rank on a node who wants to receive message from > the same remote rank must know the same receiving QP number, > and register for receiving using this QP number. > > If rank B does not register (receiving QP has been created by > another rank A on the node), and sender know B's SRQ number, > if sender sends a message to B, can B still receive this > message ? (I hope, no register, no receive) > > [Ishai] I guess that from the MPI layer prospective, the > sender can not know B's SRQ number until it ask B to give it > to him. So B can register to this QP before sending the SRQ number. > > I hope to know the opinion from other MPI team, or other XRC user. > > [Ishai] We already discussed this issues with Open MPI IB > group, and it looks fine to them. I'm sending this mail to > Prof. Panda, so he can comment on it as well. > > --CQ > > > > > -----Original Message----- > > From: Jack Morgenstein [mailto:[EMAIL PROTECTED] > > Sent: Monday, December 31, 2007 5:40 AM > > To: [EMAIL PROTECTED] > > Cc: [EMAIL PROTECTED]; Gleb Natapov; Roland Dreier; Tang, > > Changqing; [email protected] > > Subject: Re: [ofa-general] [RFC] XRC -- make receiving XRC QP > > independent of any one user process > > > > > Tang, Changqing wrote: > > > > If I have a MPI server processes on a node, many > > other MPI > > > > client processes will dynamically connect/disconnect with the > > > > server. The server use same XRC domain. > > > > > > > > Will this cause accumulating the "kernel" QP for such > > > > application ? we want the server to run 365 days a year. > > > > > > > > I have some question about the scenario above. Did you > > call for the > > > > mpi disconnect on the both ends (server/client) before > the client > > > > exit (did we must to do it?) > > > > > > Yes, both ends will call disconnect. But for us, > > MPI_Comm_disconnect() > > > call is not a collective call, it is just a local operation. > > > > > > --CQ > > > > > Possible solution (internal review as yet): > > > > Each user process registers with the XRC QP: > > a. each process registers ONCE. If it registers multiple times, > > there is no reference increment -- > > rather the registration succeeds, but only one PID entry is > > kept per QP. > > b. Can have cleanup in the event of a process dying suddenly. > > c. QP cannot be destroyed while there are any user > processes still > > registered with it. > > > > libibverbs API is as follows: > > > > ============================================================== > > ======================== > > /** > > * ibv_xrc_rcv_qp_alloc - creates an XRC QP for serving as a > > receive-side only QP, > > * and moves the created qp through the RESET->INIT and > > INIT->RTR transitions. > > * (The RTR->RTS transition is not needed, since this QP > > does no sending). > > * The sending XRC QP uses this QP as destination, while > > specifying an XRC SRQ > > * for actually receiving the transmissions and > > generating all completions on the > > * receiving side. > > * > > * This QP is created in kernel space, and persists > > until the last process registered > > * for the QP calls ibv_xrc_rcv_qp_unregister() (at > > which time the QP is destroyed). > > * > > * @pd: protection domain to use. At lower layer, this provides > > access to userspace obj > > * @xrc_domain: xrc domain to use for the QP. > > * @attr: modify-qp attributes needed to bring the QP to RTR. > > * @attr_mask: bitmap indicating which attributes are > provided in the > > attr struct. > > * used for validity checking. > > * @xrc_rcv_qpn: qp_num of created QP (if success). To be passed to > > the remote node (sender). > > * The remote node will use xrc_rcv_qpn in > > ibv_post_send when sending to > > * XRC SRQ's on this host in the same xrc domain. > > * > > * RETURNS: success (0), or a (negative) error value. > > * > > * NOTE: this verb also registers the calling user-process > with the QP > > at its creation time > > * (implicit call to ibv_xrc_rcv_qp_register), to avoid > > race conditions. > > * The creating process will need to call > > ibv_xrc_qp_unregister() for the QP to release it from > > * this process. > > */ > > > > int ibv_xrc_rcv_qp_alloc(struct ibv_pd *pd, > > struct ibv_xrc_domain *xrc_domain, > > struct ibv_qp_attr *attr, > > enum ibv_qp_attr_mask attr_mask, > > uint32_t *xrc_rcv_qpn); > > > > > ===================================================================== > > > > /** > > * ibv_xrc_rcv_qp_register: registers a user process with an XRC QP > > which serves as > > * a receive-side only QP. > > * > > * @xrc_domain: xrc domain the QP belongs to (for verification). > > * @xrc_qp_num: The (24 bit) number of the XRC QP. > > * > > * RETURNS: success (0), > > * or error (-EINVAL), if: > > * 1. There is no such QP_num allocated. > > * 2. The QP is allocated, but is not an receive XRC QP > > * 3. The XRC QP does not belong to the given domain. > > */ > > int ibv_xrc_rcv_qp_register(struct ibv_xrc_domain *xrc_domain, > > uint32_t xrc_qp_num); > > > > > ===================================================================== > > /** > > * ibv_xrc_rcv_qp_unregister: detaches a user process from > an XRC QP > > serving as > > * a receive-side only QP. If as a result, there are > > no remaining userspace processes > > * registered for this XRC QP, it is destroyed. > > * > > * @xrc_domain: xrc domain the QP belongs to (for verification). > > * @xrc_qp_num: The (24 bit) number of the XRC QP. > > * > > * RETURNS: success (0), > > * or error (-EINVAL), if: > > * 1. There is no such QP_num allocated. > > * 2. The QP is allocated, but is not an XRC QP > > * 3. The XRC QP does not belong to the given domain. > > * NOTE: I don't see any reason to return a special code if > the QP is > > destroyed -- the unregister simply > > * succeeds. > > */ > > int ibv_xrc_rcv_qp_unregister(struct ibv_xrc_domain *xrc_domain, > > uint32_t xrc_qp_num); > > ============================================================== > > =============================== > > > > Usage: > > > > 1. Sender creates an XRC QP (sending QP) 2. Sender sends some > > receiving process on a remote node (say R1) a request to provide an > > XRC QP and XRC SRQ for > > receiving messages (the request includes the sending QP number). > > 3. R1 calls ibv_xrc_rcv_qp_alloc() to create a receiving XRC QP in > > kernel space, and move > > that QP up to RTR state. This function also registers process R1 > > with the XRC QP. > > 4. R1 calls ibv_create_xrc_srq() to create an SRQ for > receive messages > > via the just created XRC QP. > > 5. R1 responds to request, providing the XRC qp number, and XRC SRQ > > number to be used in communication. > > 6. Sender then may wish to communicate with another > receiving process > > on the remote host (say R2). > > it sends a request to R2 containing the remote XRC QP number > > (obtained from R1) > > which it will use to send messages. > > 7. R2 creates an XRC SRQ (if one does not already exist for the > > domain), and also > > calls ibv_xrc_rcv_qp_register() to register the process > R2 with the > > XRC QP created by R1. > > 8. If R1 no longer needs to communicate with the sender, it calls > > ibv_xrc_rcv_qp_unregister() for the QP. > > The QP will not yet be destroyed, since R2 is still > registered with > > it. > > 9. If R2 no longer needs to communicate with the sender, it calls > > ibv_xrc_rcv_qp_unregister() for the QP. > > At this point, the QP is destroyed, since no processes remain > > registered with it. > > > > NOTES: > > 1. The problem of the QP being destroyed and quickly > re-allocated does > > not exist -- the upper bits of the > > QP number are incremented at each allocation (except for the MSB > > which is always 1 for XRC QPs). Thus, > > even if the same QP is re-allocated, its QP number > (stored in the > > QP object) will be different than > > expected (unless it is re-destroyed/re-allocated several hundred > > times). > > > > 2. With this model, we do not need a heartbeat: if a > receiving process > > dies, all XRC QPs it has registered for will > > be unregistered as part of process cleanup in kernel space. > > > > - Jack > > > > > _______________________________________________ general mailing list [email protected] http://lists.openfabrics.org/cgi-bin/mailman/listinfo/general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
