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Subject: Re: [OMPI devel] [ofa-general] [RFC] XRC -- make receiving XRC QP independent of any one user process
From: Gleb Natapov (glebn_at_[hidden])
Date: 2007-12-25 01:43:06


On Mon, Dec 24, 2007 at 11:49:37PM +0000, Tang, Changqing wrote:
>
>
> > -----Original Message-----
> > From: Pavel Shamis (Pasha) [mailto:pasha_at_[hidden]]
> > Sent: Monday, December 24, 2007 8:03 AM
> > To: Tang, Changqing
> > Cc: Jack Morgenstein; Roland Dreier;
> > general_at_[hidden]; Open MPI Developers;
> > mvapich-discuss_at_[hidden]
> > Subject: Re: [ofa-general] [RFC] XRC -- make receiving XRC QP
> > independent of any one user process
> >
> > Hi CQ,
> > 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.
Bust spec says that MPI_Comm_disconnect() is a collective call:
http://www.mpi-forum.org/docs/mpi-20-html/node114.htm#Node114

>
> --CQ
>
>
> >
> > Regards,
> > Pasha.
> > >
> > > Thanks.
> > > --CQ
> > >
> > >
> > >
> > >
> > >
> > >> -----Original Message-----
> > >> From: Pavel Shamis (Pasha) [mailto:pasha_at_[hidden]]
> > >> Sent: Thursday, December 20, 2007 9:15 AM
> > >> To: Jack Morgenstein
> > >> Cc: Tang, Changqing; Roland Dreier;
> > >> general_at_[hidden]; Open MPI Developers;
> > >> mvapich-discuss_at_[hidden]
> > >> Subject: Re: [ofa-general] [RFC] XRC -- make receiving XRC QP
> > >> independent of any one user process
> > >>
> > >> Adding Open MPI and MVAPICH community to the thread.
> > >>
> > >> Pasha (Pavel Shamis)
> > >>
> > >> Jack Morgenstein wrote:
> > >>
> > >>> background: see "XRC Cleanup order issue thread" at
> > >>>
> > >>>
> > >>>
> > >>>
> > >>
> > http://lists.openfabrics.org/pipermail/general/2007-December/043935.h
> > >> t
> > >>
> > >>> ml
> > >>>
> > >>> (userspace process which created the receiving XRC qp on a
> > >>>
> > >> given host
> > >>
> > >>> dies before other processes which still need to receive XRC
> > >>>
> > >> messages
> > >>
> > >>> on their SRQs which are "paired" with the now-destroyed
> > >>>
> > >> receiving XRC
> > >>
> > >>> QP.)
> > >>>
> > >>> Solution: Add a userspace verb (as part of the XRC suite) which
> > >>> enables the user process to create an XRC QP owned by the
> > >>>
> > >> kernel -- which belongs to the required XRC domain.
> > >>
> > >>> This QP will be destroyed when the XRC domain is closed
> > >>>
> > >> (i.e., as part
> > >>
> > >>> of a ibv_close_xrc_domain call, but only when the domain's
> > >>>
> > >> reference count goes to zero).
> > >>
> > >>> Below, I give the new userspace API for this function. Any
> > >>>
> > >> feedback will be appreciated.
> > >>
> > >>> This API will be implemented in the upcoming OFED 1.3
> > >>>
> > >> release, so we need feedback ASAP.
> > >>
> > >>> Notes:
> > >>> 1. There is no query or destroy verb for this QP. There is
> > >>>
> > >> also no userspace object for the
> > >>
> > >>> QP. Userspace has ONLY the raw qp number to use when
> > >>>
> > >> creating the (X)RC connection.
> > >>
> > >>> 2. Since the QP is "owned" by kernel space, async events
> > >>>
> > >> for this QP are also handled in kernel
> > >>
> > >>> space (i.e., reported in /var/log/messages). There are
> > >>>
> > >> no completion events for the QP, since
> > >>
> > >>> it does not send, and all receives completions are
> > >>>
> > >> reported in the XRC SRQ's cq.
> > >>
> > >>> If this QP enters the error state, the remote QP which
> > >>>
> > >> sends will start receiving RETRY_EXCEEDED
> > >>
> > >>> errors, so the application will be aware of the failure.
> > >>>
> > >>> - Jack
> > >>>
> > >>>
> > >>
> > =====================================================================
> > >> =
> > >>
> > >>> ================
> > >>> /**
> > >>> * ibv_alloc_xrc_rcv_qp - 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 XRC domain is closed.
> > >>
> > >>> * (i.e., its reference count goes to zero).
> > >>> *
> > >>> * @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. 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.
> > >>> */
> > >>>
> > >>> int ibv_alloc_xrc_rcv_qp(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);
> > >>>
> > >>> Notes:
> > >>>
> > >>> 1. Although the kernel creates the qp in the kernel's own
> > >>>
> > >> PD, we still need the PD
> > >>
> > >>> parameter to determine the device.
> > >>>
> > >>> 2. I chose to use struct ibv_qp_attr, which is used in
> > >>>
> > >> modify QP, rather than create
> > >>
> > >>> a new structure for this purpose. This also guards
> > >>>
> > >> against API changes in the event
> > >>
> > >>> that during development I notice that more modify-qp
> > >>>
> > >> parameters must be specified
> > >>
> > >>> for this operation to work.
> > >>>
> > >>> 3. Table of the ibv_qp_attr parameters showing what values to set:
> > >>>
> > >>> struct ibv_qp_attr {
> > >>> enum ibv_qp_state qp_state; Not needed
> > >>> enum ibv_qp_state cur_qp_state; Not needed
> > >>> -- Driver starts from RESET and takes qp to RTR.
> > >>> enum ibv_mtu path_mtu; Yes
> > >>> enum ibv_mig_state path_mig_state; Yes
> > >>> uint32_t qkey; Yes
> > >>> uint32_t rq_psn; Yes
> > >>> uint32_t sq_psn; Not needed
> > >>> uint32_t dest_qp_num; Yes
> > >>>
> > >> -- this is the remote side QP for the RC conn.
> > >>
> > >>> int qp_access_flags; Yes
> > >>> struct ibv_qp_cap cap; Need
> > >>>
> > >> only XRC domain.
> > >>
> > >>> Other
> > >>>
> > >> caps will use hard-coded values:
> > >>
> > >> max_send_wr = 1;
> > >>
> > >> max_recv_wr = 0;
> > >>
> > >> max_send_sge = 1;
> > >>
> > >> max_recv_sge = 0;
> > >>
> > >> max_inline_data = 0;
> > >>
> > >>> struct ibv_ah_attr ah_attr; Yes
> > >>> struct ibv_ah_attr alt_ah_attr; Optional
> > >>> uint16_t pkey_index; Yes
> > >>> uint16_t alt_pkey_index; Optional
> > >>> uint8_t en_sqd_async_notify; Not
> > >>>
> > >> needed (No sq)
> > >>
> > >>> uint8_t sq_draining; Not
> > >>>
> > >> needed (No sq)
> > >>
> > >>> uint8_t max_rd_atomic; Not
> > >>>
> > >> needed (No sq)
> > >>
> > >>> uint8_t max_dest_rd_atomic; Yes
> > >>>
> > >> -- Total max outstanding RDMAs expected
> > >>
> > >>> for
> > >>>
> > >> ALL srq destinations using this receive QP.
> > >>
> > >>> (if
> > >>>
> > >> you are only using SENDs, this value can be 0).
> > >>
> > >>> uint8_t min_rnr_timer; default - 0
> > >>> uint8_t port_num; Yes
> > >>> uint8_t timeout; Yes
> > >>> uint8_t retry_cnt; Yes
> > >>> uint8_t rnr_retry; Yes
> > >>> uint8_t alt_port_num; Optional
> > >>> uint8_t alt_timeout; Optional
> > >>> };
> > >>>
> > >>> 4. Attribute mask bits to set:
> > >>> For RESET_to_INIT transition:
> > >>> IB_QP_ACCESS_FLAGS | IB_QP_PKEY_INDEX | IB_QP_PORT
> > >>>
> > >>> For INIT_to_RTR transition:
> > >>> IB_QP_AV | IB_QP_PATH_MTU |
> > >>> IB_QP_DEST_QPN | IB_QP_RQ_PSN | IB_QP_MIN_RNR_TIMER
> > >>> If you are using RDMA or atomics, also set:
> > >>> IB_QP_MAX_DEST_RD_ATOMIC
> > >>>
> > >>>
> > >>> _______________________________________________
> > >>> general mailing list
> > >>> general_at_[hidden]
> > >>> http://lists.openfabrics.org/cgi-bin/mailman/listinfo/general
> > >>>
> > >>> To unsubscribe, please visit
> > >>> http://openib.org/mailman/listinfo/openib-general
> > >>>
> > >>>
> > >>>
> > >> --
> > >> Pavel Shamis (Pasha)
> > >> Mellanox Technologies
> > >>
> > >>
> > >>
> > >
> > >
> >
> >
> > --
> > Pavel Shamis (Pasha)
> > Mellanox Technologies
> >
> >
> _______________________________________________
> general mailing list
> general_at_[hidden]
> http://lists.openfabrics.org/cgi-bin/mailman/listinfo/general
>
> To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general

--
			Gleb.