Merge remote-tracking branch 'rdma/for-next'

[karo-tx-linux.git] / net / rds / ib_send.c

/*
 * Copyright (c) 2006 Oracle.  All rights reserved.
 *
 * This software is available to you under a choice of one of two
 * licenses.  You may choose to be licensed under the terms of the GNU
 * General Public License (GPL) Version 2, available from the file
 * COPYING in the main directory of this source tree, or the
 * OpenIB.org BSD license below:
 *
 *     Redistribution and use in source and binary forms, with or
 *     without modification, are permitted provided that the following
 *     conditions are met:
 *
 *      - Redistributions of source code must retain the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer.
 *
 *      - Redistributions in binary form must reproduce the above
 *        copyright notice, this list of conditions and the following
 *        disclaimer in the documentation and/or other materials
 *        provided with the distribution.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 */
#include <linux/kernel.h>
#include <linux/in.h>
#include <linux/device.h>
#include <linux/dmapool.h>
#include <linux/ratelimit.h>

#include "rds.h"
#include "ib.h"

/*
 * Convert IB-specific error message to RDS error message and call core
 * completion handler.
 */
static void rds_ib_send_complete(struct rds_message *rm,
                                 int wc_status,
                                 void (*complete)(struct rds_message *rm, int status))
{
        int notify_status;

        switch (wc_status) {
        case IB_WC_WR_FLUSH_ERR:
                return;

        case IB_WC_SUCCESS:
                notify_status = RDS_RDMA_SUCCESS;
                break;

        case IB_WC_REM_ACCESS_ERR:
                notify_status = RDS_RDMA_REMOTE_ERROR;
                break;

        default:
                notify_status = RDS_RDMA_OTHER_ERROR;
                break;
        }
        complete(rm, notify_status);
}

static void rds_ib_send_unmap_data(struct rds_ib_connection *ic,
                                   struct rm_data_op *op,
                                   int wc_status)
{
        if (op->op_nents)
                ib_dma_unmap_sg(ic->i_cm_id->device,
                                op->op_sg, op->op_nents,
                                DMA_TO_DEVICE);
}

static void rds_ib_send_unmap_rdma(struct rds_ib_connection *ic,
                                   struct rm_rdma_op *op,
                                   int wc_status)
{
        if (op->op_mapped) {
                ib_dma_unmap_sg(ic->i_cm_id->device,
                                op->op_sg, op->op_nents,
                                op->op_write ? DMA_TO_DEVICE : DMA_FROM_DEVICE);
                op->op_mapped = 0;
        }

        /* If the user asked for a completion notification on this
         * message, we can implement three different semantics:
         *  1.  Notify when we received the ACK on the RDS message
         *      that was queued with the RDMA. This provides reliable
         *      notification of RDMA status at the expense of a one-way
         *      packet delay.
         *  2.  Notify when the IB stack gives us the completion event for
         *      the RDMA operation.
         *  3.  Notify when the IB stack gives us the completion event for
         *      the accompanying RDS messages.
         * Here, we implement approach #3. To implement approach #2,
         * we would need to take an event for the rdma WR. To implement #1,
         * don't call rds_rdma_send_complete at all, and fall back to the notify
         * handling in the ACK processing code.
         *
         * Note: There's no need to explicitly sync any RDMA buffers using
         * ib_dma_sync_sg_for_cpu - the completion for the RDMA
         * operation itself unmapped the RDMA buffers, which takes care
         * of synching.
         */
        rds_ib_send_complete(container_of(op, struct rds_message, rdma),
                             wc_status, rds_rdma_send_complete);

        if (op->op_write)
                rds_stats_add(s_send_rdma_bytes, op->op_bytes);
        else
                rds_stats_add(s_recv_rdma_bytes, op->op_bytes);
}

static void rds_ib_send_unmap_atomic(struct rds_ib_connection *ic,
                                     struct rm_atomic_op *op,
                                     int wc_status)
{
        /* unmap atomic recvbuf */
        if (op->op_mapped) {
                ib_dma_unmap_sg(ic->i_cm_id->device, op->op_sg, 1,
                                DMA_FROM_DEVICE);
                op->op_mapped = 0;
        }

        rds_ib_send_complete(container_of(op, struct rds_message, atomic),
                             wc_status, rds_atomic_send_complete);

        if (op->op_type == RDS_ATOMIC_TYPE_CSWP)
                rds_ib_stats_inc(s_ib_atomic_cswp);
        else
                rds_ib_stats_inc(s_ib_atomic_fadd);
}

/*
 * Unmap the resources associated with a struct send_work.
 *
 * Returns the rm for no good reason other than it is unobtainable
 * other than by switching on wr.opcode, currently, and the caller,
 * the event handler, needs it.
 */
static struct rds_message *rds_ib_send_unmap_op(struct rds_ib_connection *ic,
                                                struct rds_ib_send_work *send,
                                                int wc_status)
{
        struct rds_message *rm = NULL;

        /* In the error case, wc.opcode sometimes contains garbage */
        switch (send->s_wr.opcode) {
        case IB_WR_SEND:
                if (send->s_op) {
                        rm = container_of(send->s_op, struct rds_message, data);
                        rds_ib_send_unmap_data(ic, send->s_op, wc_status);
                }
                break;
        case IB_WR_RDMA_WRITE:
        case IB_WR_RDMA_READ:
                if (send->s_op) {
                        rm = container_of(send->s_op, struct rds_message, rdma);
                        rds_ib_send_unmap_rdma(ic, send->s_op, wc_status);
                }
                break;
        case IB_WR_ATOMIC_FETCH_AND_ADD:
        case IB_WR_ATOMIC_CMP_AND_SWP:
                if (send->s_op) {
                        rm = container_of(send->s_op, struct rds_message, atomic);
                        rds_ib_send_unmap_atomic(ic, send->s_op, wc_status);
                }
                break;
        default:
                printk_ratelimited(KERN_NOTICE
                               "RDS/IB: %s: unexpected opcode 0x%x in WR!\n",
                               __func__, send->s_wr.opcode);
                break;
        }

        send->s_wr.opcode = 0xdead;

        return rm;
}

void rds_ib_send_init_ring(struct rds_ib_connection *ic)
{
        struct rds_ib_send_work *send;
        u32 i;

        for (i = 0, send = ic->i_sends; i < ic->i_send_ring.w_nr; i++, send++) {
                struct ib_sge *sge;

                send->s_op = NULL;

                send->s_wr.wr_id = i | RDS_IB_SEND_OP;
                send->s_wr.sg_list = send->s_sge;
                send->s_wr.ex.imm_data = 0;

                sge = &send->s_sge[0];
                sge->addr = ic->i_send_hdrs_dma + (i * sizeof(struct rds_header));
                sge->length = sizeof(struct rds_header);
                sge->lkey = ic->i_pd->local_dma_lkey;

                send->s_sge[1].lkey = ic->i_pd->local_dma_lkey;
        }
}

void rds_ib_send_clear_ring(struct rds_ib_connection *ic)
{
        struct rds_ib_send_work *send;
        u32 i;

        for (i = 0, send = ic->i_sends; i < ic->i_send_ring.w_nr; i++, send++) {
                if (send->s_op && send->s_wr.opcode != 0xdead)
                        rds_ib_send_unmap_op(ic, send, IB_WC_WR_FLUSH_ERR);
        }
}

/*
 * The only fast path caller always has a non-zero nr, so we don't
 * bother testing nr before performing the atomic sub.
 */
static void rds_ib_sub_signaled(struct rds_ib_connection *ic, int nr)
{
        if ((atomic_sub_return(nr, &ic->i_signaled_sends) == 0) &&
            waitqueue_active(&rds_ib_ring_empty_wait))
                wake_up(&rds_ib_ring_empty_wait);
        BUG_ON(atomic_read(&ic->i_signaled_sends) < 0);
}

/*
 * The _oldest/_free ring operations here race cleanly with the alloc/unalloc
 * operations performed in the send path.  As the sender allocs and potentially
 * unallocs the next free entry in the ring it doesn't alter which is
 * the next to be freed, which is what this is concerned with.
 */
void rds_ib_send_cqe_handler(struct rds_ib_connection *ic, struct ib_wc *wc)
{
        struct rds_message *rm = NULL;
        struct rds_connection *conn = ic->conn;
        struct rds_ib_send_work *send;
        u32 completed;
        u32 oldest;
        u32 i = 0;
        int nr_sig = 0;


        rdsdebug("wc wr_id 0x%llx status %u (%s) byte_len %u imm_data %u\n",
                 (unsigned long long)wc->wr_id, wc->status,
                 ib_wc_status_msg(wc->status), wc->byte_len,
                 be32_to_cpu(wc->ex.imm_data));
        rds_ib_stats_inc(s_ib_tx_cq_event);

        if (wc->wr_id == RDS_IB_ACK_WR_ID) {
                if (time_after(jiffies, ic->i_ack_queued + HZ / 2))
                        rds_ib_stats_inc(s_ib_tx_stalled);
                rds_ib_ack_send_complete(ic);
                return;
        }

        oldest = rds_ib_ring_oldest(&ic->i_send_ring);

        completed = rds_ib_ring_completed(&ic->i_send_ring,
                                          (wc->wr_id & ~RDS_IB_SEND_OP),
                                          oldest);

        for (i = 0; i < completed; i++) {
                send = &ic->i_sends[oldest];
                if (send->s_wr.send_flags & IB_SEND_SIGNALED)
                        nr_sig++;

                rm = rds_ib_send_unmap_op(ic, send, wc->status);

                if (time_after(jiffies, send->s_queued + HZ / 2))
                        rds_ib_stats_inc(s_ib_tx_stalled);

                if (send->s_op) {
                        if (send->s_op == rm->m_final_op) {
                                /* If anyone waited for this message to get
                                 * flushed out, wake them up now
                                 */
                                rds_message_unmapped(rm);
                        }
                        rds_message_put(rm);
                        send->s_op = NULL;
                }

                oldest = (oldest + 1) % ic->i_send_ring.w_nr;
        }

        rds_ib_ring_free(&ic->i_send_ring, completed);
        rds_ib_sub_signaled(ic, nr_sig);
        nr_sig = 0;

        if (test_and_clear_bit(RDS_LL_SEND_FULL, &conn->c_flags) ||
            test_bit(0, &conn->c_map_queued))
                queue_delayed_work(rds_wq, &conn->c_send_w, 0);

        /* We expect errors as the qp is drained during shutdown */
        if (wc->status != IB_WC_SUCCESS && rds_conn_up(conn)) {
                rds_ib_conn_error(conn, "send completion on %pI4 had status %u (%s), disconnecting and reconnecting\n",
                                  &conn->c_faddr, wc->status,
                                  ib_wc_status_msg(wc->status));
        }
}

/*
 * This is the main function for allocating credits when sending
 * messages.
 *
 * Conceptually, we have two counters:
 *  -   send credits: this tells us how many WRs we're allowed
 *      to submit without overruning the receiver's queue. For
 *      each SEND WR we post, we decrement this by one.
 *
 *  -   posted credits: this tells us how many WRs we recently
 *      posted to the receive queue. This value is transferred
 *      to the peer as a "credit update" in a RDS header field.
 *      Every time we transmit credits to the peer, we subtract
 *      the amount of transferred credits from this counter.
 *
 * It is essential that we avoid situations where both sides have
 * exhausted their send credits, and are unable to send new credits
 * to the peer. We achieve this by requiring that we send at least
 * one credit update to the peer before exhausting our credits.
 * When new credits arrive, we subtract one credit that is withheld
 * until we've posted new buffers and are ready to transmit these
 * credits (see rds_ib_send_add_credits below).
 *
 * The RDS send code is essentially single-threaded; rds_send_xmit
 * sets RDS_IN_XMIT to ensure exclusive access to the send ring.
 * However, the ACK sending code is independent and can race with
 * message SENDs.
 *
 * In the send path, we need to update the counters for send credits
 * and the counter of posted buffers atomically - when we use the
 * last available credit, we cannot allow another thread to race us
 * and grab the posted credits counter.  Hence, we have to use a
 * spinlock to protect the credit counter, or use atomics.
 *
 * Spinlocks shared between the send and the receive path are bad,
 * because they create unnecessary delays. An early implementation
 * using a spinlock showed a 5% degradation in throughput at some
 * loads.
 *
 * This implementation avoids spinlocks completely, putting both
 * counters into a single atomic, and updating that atomic using
 * atomic_add (in the receive path, when receiving fresh credits),
 * and using atomic_cmpxchg when updating the two counters.
 */
int rds_ib_send_grab_credits(struct rds_ib_connection *ic,
                             u32 wanted, u32 *adv_credits, int need_posted, int max_posted)
{
        unsigned int avail, posted, got = 0, advertise;
        long oldval, newval;

        *adv_credits = 0;
        if (!ic->i_flowctl)
                return wanted;

try_again:
        advertise = 0;
        oldval = newval = atomic_read(&ic->i_credits);
        posted = IB_GET_POST_CREDITS(oldval);
        avail = IB_GET_SEND_CREDITS(oldval);

        rdsdebug("wanted=%u credits=%u posted=%u\n",
                        wanted, avail, posted);

        /* The last credit must be used to send a credit update. */
        if (avail && !posted)
                avail--;

        if (avail < wanted) {
                struct rds_connection *conn = ic->i_cm_id->context;

                /* Oops, there aren't that many credits left! */
                set_bit(RDS_LL_SEND_FULL, &conn->c_flags);
                got = avail;
        } else {
                /* Sometimes you get what you want, lalala. */
                got = wanted;
        }
        newval -= IB_SET_SEND_CREDITS(got);

        /*
         * If need_posted is non-zero, then the caller wants
         * the posted regardless of whether any send credits are
         * available.
         */
        if (posted && (got || need_posted)) {
                advertise = min_t(unsigned int, posted, max_posted);
                newval -= IB_SET_POST_CREDITS(advertise);
        }

        /* Finally bill everything */
        if (atomic_cmpxchg(&ic->i_credits, oldval, newval) != oldval)
                goto try_again;

        *adv_credits = advertise;
        return got;
}

void rds_ib_send_add_credits(struct rds_connection *conn, unsigned int credits)
{
        struct rds_ib_connection *ic = conn->c_transport_data;

        if (credits == 0)
                return;

        rdsdebug("credits=%u current=%u%s\n",
                        credits,
                        IB_GET_SEND_CREDITS(atomic_read(&ic->i_credits)),
                        test_bit(RDS_LL_SEND_FULL, &conn->c_flags) ? ", ll_send_full" : "");

        atomic_add(IB_SET_SEND_CREDITS(credits), &ic->i_credits);
        if (test_and_clear_bit(RDS_LL_SEND_FULL, &conn->c_flags))
                queue_delayed_work(rds_wq, &conn->c_send_w, 0);

        WARN_ON(IB_GET_SEND_CREDITS(credits) >= 16384);

        rds_ib_stats_inc(s_ib_rx_credit_updates);
}

void rds_ib_advertise_credits(struct rds_connection *conn, unsigned int posted)
{
        struct rds_ib_connection *ic = conn->c_transport_data;

        if (posted == 0)
                return;

        atomic_add(IB_SET_POST_CREDITS(posted), &ic->i_credits);

        /* Decide whether to send an update to the peer now.
         * If we would send a credit update for every single buffer we
         * post, we would end up with an ACK storm (ACK arrives,
         * consumes buffer, we refill the ring, send ACK to remote
         * advertising the newly posted buffer... ad inf)
         *
         * Performance pretty much depends on how often we send
         * credit updates - too frequent updates mean lots of ACKs.
         * Too infrequent updates, and the peer will run out of
         * credits and has to throttle.
         * For the time being, 16 seems to be a good compromise.
         */
        if (IB_GET_POST_CREDITS(atomic_read(&ic->i_credits)) >= 16)
                set_bit(IB_ACK_REQUESTED, &ic->i_ack_flags);
}

static inline int rds_ib_set_wr_signal_state(struct rds_ib_connection *ic,
                                             struct rds_ib_send_work *send,
                                             bool notify)
{
        /*
         * We want to delay signaling completions just enough to get
         * the batching benefits but not so much that we create dead time
         * on the wire.
         */
        if (ic->i_unsignaled_wrs-- == 0 || notify) {
                ic->i_unsignaled_wrs = rds_ib_sysctl_max_unsig_wrs;
                send->s_wr.send_flags |= IB_SEND_SIGNALED;
                return 1;
        }
        return 0;
}

/*
 * This can be called multiple times for a given message.  The first time
 * we see a message we map its scatterlist into the IB device so that
 * we can provide that mapped address to the IB scatter gather entries
 * in the IB work requests.  We translate the scatterlist into a series
 * of work requests that fragment the message.  These work requests complete
 * in order so we pass ownership of the message to the completion handler
 * once we send the final fragment.
 *
 * The RDS core uses the c_send_lock to only enter this function once
 * per connection.  This makes sure that the tx ring alloc/unalloc pairs
 * don't get out of sync and confuse the ring.
 */
int rds_ib_xmit(struct rds_connection *conn, struct rds_message *rm,
                unsigned int hdr_off, unsigned int sg, unsigned int off)
{
        struct rds_ib_connection *ic = conn->c_transport_data;
        struct ib_device *dev = ic->i_cm_id->device;
        struct rds_ib_send_work *send = NULL;
        struct rds_ib_send_work *first;
        struct rds_ib_send_work *prev;
        struct ib_send_wr *failed_wr;
        struct scatterlist *scat;
        u32 pos;
        u32 i;
        u32 work_alloc;
        u32 credit_alloc = 0;
        u32 posted;
        u32 adv_credits = 0;
        int send_flags = 0;
        int bytes_sent = 0;
        int ret;
        int flow_controlled = 0;
        int nr_sig = 0;

        BUG_ON(off % RDS_FRAG_SIZE);
        BUG_ON(hdr_off != 0 && hdr_off != sizeof(struct rds_header));

        /* Do not send cong updates to IB loopback */
        if (conn->c_loopback
            && rm->m_inc.i_hdr.h_flags & RDS_FLAG_CONG_BITMAP) {
                rds_cong_map_updated(conn->c_fcong, ~(u64) 0);
                scat = &rm->data.op_sg[sg];
                ret = max_t(int, RDS_CONG_MAP_BYTES, scat->length);
                return sizeof(struct rds_header) + ret;
        }

        /* FIXME we may overallocate here */
        if (be32_to_cpu(rm->m_inc.i_hdr.h_len) == 0)
                i = 1;
        else
                i = ceil(be32_to_cpu(rm->m_inc.i_hdr.h_len), RDS_FRAG_SIZE);

        work_alloc = rds_ib_ring_alloc(&ic->i_send_ring, i, &pos);
        if (work_alloc == 0) {
                set_bit(RDS_LL_SEND_FULL, &conn->c_flags);
                rds_ib_stats_inc(s_ib_tx_ring_full);
                ret = -ENOMEM;
                goto out;
        }

        if (ic->i_flowctl) {
                credit_alloc = rds_ib_send_grab_credits(ic, work_alloc, &posted, 0, RDS_MAX_ADV_CREDIT);
                adv_credits += posted;
                if (credit_alloc < work_alloc) {
                        rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc - credit_alloc);
                        work_alloc = credit_alloc;
                        flow_controlled = 1;
                }
                if (work_alloc == 0) {
                        set_bit(RDS_LL_SEND_FULL, &conn->c_flags);
                        rds_ib_stats_inc(s_ib_tx_throttle);
                        ret = -ENOMEM;
                        goto out;
                }
        }

        /* map the message the first time we see it */
        if (!ic->i_data_op) {
                if (rm->data.op_nents) {
                        rm->data.op_count = ib_dma_map_sg(dev,
                                                          rm->data.op_sg,
                                                          rm->data.op_nents,
                                                          DMA_TO_DEVICE);
                        rdsdebug("ic %p mapping rm %p: %d\n", ic, rm, rm->data.op_count);
                        if (rm->data.op_count == 0) {
                                rds_ib_stats_inc(s_ib_tx_sg_mapping_failure);
                                rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc);
                                ret = -ENOMEM; /* XXX ? */
                                goto out;
                        }
                } else {
                        rm->data.op_count = 0;
                }

                rds_message_addref(rm);
                rm->data.op_dmasg = 0;
                rm->data.op_dmaoff = 0;
                ic->i_data_op = &rm->data;

                /* Finalize the header */
                if (test_bit(RDS_MSG_ACK_REQUIRED, &rm->m_flags))
                        rm->m_inc.i_hdr.h_flags |= RDS_FLAG_ACK_REQUIRED;
                if (test_bit(RDS_MSG_RETRANSMITTED, &rm->m_flags))
                        rm->m_inc.i_hdr.h_flags |= RDS_FLAG_RETRANSMITTED;

                /* If it has a RDMA op, tell the peer we did it. This is
                 * used by the peer to release use-once RDMA MRs. */
                if (rm->rdma.op_active) {
                        struct rds_ext_header_rdma ext_hdr;

                        ext_hdr.h_rdma_rkey = cpu_to_be32(rm->rdma.op_rkey);
                        rds_message_add_extension(&rm->m_inc.i_hdr,
                                        RDS_EXTHDR_RDMA, &ext_hdr, sizeof(ext_hdr));
                }
                if (rm->m_rdma_cookie) {
                        rds_message_add_rdma_dest_extension(&rm->m_inc.i_hdr,
                                        rds_rdma_cookie_key(rm->m_rdma_cookie),
                                        rds_rdma_cookie_offset(rm->m_rdma_cookie));
                }

                /* Note - rds_ib_piggyb_ack clears the ACK_REQUIRED bit, so
                 * we should not do this unless we have a chance of at least
                 * sticking the header into the send ring. Which is why we
                 * should call rds_ib_ring_alloc first. */
                rm->m_inc.i_hdr.h_ack = cpu_to_be64(rds_ib_piggyb_ack(ic));
                rds_message_make_checksum(&rm->m_inc.i_hdr);

                /*
                 * Update adv_credits since we reset the ACK_REQUIRED bit.
                 */
                if (ic->i_flowctl) {
                        rds_ib_send_grab_credits(ic, 0, &posted, 1, RDS_MAX_ADV_CREDIT - adv_credits);
                        adv_credits += posted;
                        BUG_ON(adv_credits > 255);
                }
        }

        /* Sometimes you want to put a fence between an RDMA
         * READ and the following SEND.
         * We could either do this all the time
         * or when requested by the user. Right now, we let
         * the application choose.
         */
        if (rm->rdma.op_active && rm->rdma.op_fence)
                send_flags = IB_SEND_FENCE;

        /* Each frag gets a header. Msgs may be 0 bytes */
        send = &ic->i_sends[pos];
        first = send;
        prev = NULL;
        scat = &ic->i_data_op->op_sg[rm->data.op_dmasg];
        i = 0;
        do {
                unsigned int len = 0;

                /* Set up the header */
                send->s_wr.send_flags = send_flags;
                send->s_wr.opcode = IB_WR_SEND;
                send->s_wr.num_sge = 1;
                send->s_wr.next = NULL;
                send->s_queued = jiffies;
                send->s_op = NULL;

                send->s_sge[0].addr = ic->i_send_hdrs_dma
                        + (pos * sizeof(struct rds_header));
                send->s_sge[0].length = sizeof(struct rds_header);

                memcpy(&ic->i_send_hdrs[pos], &rm->m_inc.i_hdr, sizeof(struct rds_header));

                /* Set up the data, if present */
                if (i < work_alloc
                    && scat != &rm->data.op_sg[rm->data.op_count]) {
                        len = min(RDS_FRAG_SIZE,
                                ib_sg_dma_len(dev, scat) - rm->data.op_dmaoff);
                        send->s_wr.num_sge = 2;

                        send->s_sge[1].addr = ib_sg_dma_address(dev, scat);
                        send->s_sge[1].addr += rm->data.op_dmaoff;
                        send->s_sge[1].length = len;

                        bytes_sent += len;
                        rm->data.op_dmaoff += len;
                        if (rm->data.op_dmaoff == ib_sg_dma_len(dev, scat)) {
                                scat++;
                                rm->data.op_dmasg++;
                                rm->data.op_dmaoff = 0;
                        }
                }

                rds_ib_set_wr_signal_state(ic, send, 0);

                /*
                 * Always signal the last one if we're stopping due to flow control.
                 */
                if (ic->i_flowctl && flow_controlled && i == (work_alloc-1))
                        send->s_wr.send_flags |= IB_SEND_SIGNALED | IB_SEND_SOLICITED;

                if (send->s_wr.send_flags & IB_SEND_SIGNALED)
                        nr_sig++;

                rdsdebug("send %p wr %p num_sge %u next %p\n", send,
                         &send->s_wr, send->s_wr.num_sge, send->s_wr.next);

                if (ic->i_flowctl && adv_credits) {
                        struct rds_header *hdr = &ic->i_send_hdrs[pos];

                        /* add credit and redo the header checksum */
                        hdr->h_credit = adv_credits;
                        rds_message_make_checksum(hdr);
                        adv_credits = 0;
                        rds_ib_stats_inc(s_ib_tx_credit_updates);
                }

                if (prev)
                        prev->s_wr.next = &send->s_wr;
                prev = send;

                pos = (pos + 1) % ic->i_send_ring.w_nr;
                send = &ic->i_sends[pos];
                i++;

        } while (i < work_alloc
                 && scat != &rm->data.op_sg[rm->data.op_count]);

        /* Account the RDS header in the number of bytes we sent, but just once.
         * The caller has no concept of fragmentation. */
        if (hdr_off == 0)
                bytes_sent += sizeof(struct rds_header);

        /* if we finished the message then send completion owns it */
        if (scat == &rm->data.op_sg[rm->data.op_count]) {
                prev->s_op = ic->i_data_op;
                prev->s_wr.send_flags |= IB_SEND_SOLICITED;
                if (!(prev->s_wr.send_flags & IB_SEND_SIGNALED)) {
                        ic->i_unsignaled_wrs = rds_ib_sysctl_max_unsig_wrs;
                        prev->s_wr.send_flags |= IB_SEND_SIGNALED;
                        nr_sig++;
                }
                ic->i_data_op = NULL;
        }

        /* Put back wrs & credits we didn't use */
        if (i < work_alloc) {
                rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc - i);
                work_alloc = i;
        }
        if (ic->i_flowctl && i < credit_alloc)
                rds_ib_send_add_credits(conn, credit_alloc - i);

        if (nr_sig)
                atomic_add(nr_sig, &ic->i_signaled_sends);

        /* XXX need to worry about failed_wr and partial sends. */
        failed_wr = &first->s_wr;
        ret = ib_post_send(ic->i_cm_id->qp, &first->s_wr, &failed_wr);
        rdsdebug("ic %p first %p (wr %p) ret %d wr %p\n", ic,
                 first, &first->s_wr, ret, failed_wr);
        BUG_ON(failed_wr != &first->s_wr);
        if (ret) {
                printk(KERN_WARNING "RDS/IB: ib_post_send to %pI4 "
                       "returned %d\n", &conn->c_faddr, ret);
                rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc);
                rds_ib_sub_signaled(ic, nr_sig);
                if (prev->s_op) {
                        ic->i_data_op = prev->s_op;
                        prev->s_op = NULL;
                }

                rds_ib_conn_error(ic->conn, "ib_post_send failed\n");
                goto out;
        }

        ret = bytes_sent;
out:
        BUG_ON(adv_credits);
        return ret;
}

/*
 * Issue atomic operation.
 * A simplified version of the rdma case, we always map 1 SG, and
 * only 8 bytes, for the return value from the atomic operation.
 */
int rds_ib_xmit_atomic(struct rds_connection *conn, struct rm_atomic_op *op)
{
        struct rds_ib_connection *ic = conn->c_transport_data;
        struct rds_ib_send_work *send = NULL;
        struct ib_send_wr *failed_wr;
        struct rds_ib_device *rds_ibdev;
        u32 pos;
        u32 work_alloc;
        int ret;
        int nr_sig = 0;

        rds_ibdev = ib_get_client_data(ic->i_cm_id->device, &rds_ib_client);

        work_alloc = rds_ib_ring_alloc(&ic->i_send_ring, 1, &pos);
        if (work_alloc != 1) {
                rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc);
                rds_ib_stats_inc(s_ib_tx_ring_full);
                ret = -ENOMEM;
                goto out;
        }

        /* address of send request in ring */
        send = &ic->i_sends[pos];
        send->s_queued = jiffies;

        if (op->op_type == RDS_ATOMIC_TYPE_CSWP) {
                send->s_atomic_wr.wr.opcode = IB_WR_MASKED_ATOMIC_CMP_AND_SWP;
                send->s_atomic_wr.compare_add = op->op_m_cswp.compare;
                send->s_atomic_wr.swap = op->op_m_cswp.swap;
                send->s_atomic_wr.compare_add_mask = op->op_m_cswp.compare_mask;
                send->s_atomic_wr.swap_mask = op->op_m_cswp.swap_mask;
        } else { /* FADD */
                send->s_atomic_wr.wr.opcode = IB_WR_MASKED_ATOMIC_FETCH_AND_ADD;
                send->s_atomic_wr.compare_add = op->op_m_fadd.add;
                send->s_atomic_wr.swap = 0;
                send->s_atomic_wr.compare_add_mask = op->op_m_fadd.nocarry_mask;
                send->s_atomic_wr.swap_mask = 0;
        }
        nr_sig = rds_ib_set_wr_signal_state(ic, send, op->op_notify);
        send->s_atomic_wr.wr.num_sge = 1;
        send->s_atomic_wr.wr.next = NULL;
        send->s_atomic_wr.remote_addr = op->op_remote_addr;
        send->s_atomic_wr.rkey = op->op_rkey;
        send->s_op = op;
        rds_message_addref(container_of(send->s_op, struct rds_message, atomic));

        /* map 8 byte retval buffer to the device */
        ret = ib_dma_map_sg(ic->i_cm_id->device, op->op_sg, 1, DMA_FROM_DEVICE);
        rdsdebug("ic %p mapping atomic op %p. mapped %d pg\n", ic, op, ret);
        if (ret != 1) {
                rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc);
                rds_ib_stats_inc(s_ib_tx_sg_mapping_failure);
                ret = -ENOMEM; /* XXX ? */
                goto out;
        }

        /* Convert our struct scatterlist to struct ib_sge */
        send->s_sge[0].addr = ib_sg_dma_address(ic->i_cm_id->device, op->op_sg);
        send->s_sge[0].length = ib_sg_dma_len(ic->i_cm_id->device, op->op_sg);
        send->s_sge[0].lkey = ic->i_pd->local_dma_lkey;

        rdsdebug("rva %Lx rpa %Lx len %u\n", op->op_remote_addr,
                 send->s_sge[0].addr, send->s_sge[0].length);

        if (nr_sig)
                atomic_add(nr_sig, &ic->i_signaled_sends);

        failed_wr = &send->s_atomic_wr.wr;
        ret = ib_post_send(ic->i_cm_id->qp, &send->s_atomic_wr.wr, &failed_wr);
        rdsdebug("ic %p send %p (wr %p) ret %d wr %p\n", ic,
                 send, &send->s_atomic_wr, ret, failed_wr);
        BUG_ON(failed_wr != &send->s_atomic_wr.wr);
        if (ret) {
                printk(KERN_WARNING "RDS/IB: atomic ib_post_send to %pI4 "
                       "returned %d\n", &conn->c_faddr, ret);
                rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc);
                rds_ib_sub_signaled(ic, nr_sig);
                goto out;
        }

        if (unlikely(failed_wr != &send->s_atomic_wr.wr)) {
                printk(KERN_WARNING "RDS/IB: atomic ib_post_send() rc=%d, but failed_wqe updated!\n", ret);
                BUG_ON(failed_wr != &send->s_atomic_wr.wr);
        }

out:
        return ret;
}

int rds_ib_xmit_rdma(struct rds_connection *conn, struct rm_rdma_op *op)
{
        struct rds_ib_connection *ic = conn->c_transport_data;
        struct rds_ib_send_work *send = NULL;
        struct rds_ib_send_work *first;
        struct rds_ib_send_work *prev;
        struct ib_send_wr *failed_wr;
        struct scatterlist *scat;
        unsigned long len;
        u64 remote_addr = op->op_remote_addr;
        u32 max_sge = ic->rds_ibdev->max_sge;
        u32 pos;
        u32 work_alloc;
        u32 i;
        u32 j;
        int sent;
        int ret;
        int num_sge;
        int nr_sig = 0;

        /* map the op the first time we see it */
        if (!op->op_mapped) {
                op->op_count = ib_dma_map_sg(ic->i_cm_id->device,
                                             op->op_sg, op->op_nents, (op->op_write) ?
                                             DMA_TO_DEVICE : DMA_FROM_DEVICE);
                rdsdebug("ic %p mapping op %p: %d\n", ic, op, op->op_count);
                if (op->op_count == 0) {
                        rds_ib_stats_inc(s_ib_tx_sg_mapping_failure);
                        ret = -ENOMEM; /* XXX ? */
                        goto out;
                }

                op->op_mapped = 1;
        }

        /*
         * Instead of knowing how to return a partial rdma read/write we insist that there
         * be enough work requests to send the entire message.
         */
        i = ceil(op->op_count, max_sge);

        work_alloc = rds_ib_ring_alloc(&ic->i_send_ring, i, &pos);
        if (work_alloc != i) {
                rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc);
                rds_ib_stats_inc(s_ib_tx_ring_full);
                ret = -ENOMEM;
                goto out;
        }

        send = &ic->i_sends[pos];
        first = send;
        prev = NULL;
        scat = &op->op_sg[0];
        sent = 0;
        num_sge = op->op_count;

        for (i = 0; i < work_alloc && scat != &op->op_sg[op->op_count]; i++) {
                send->s_wr.send_flags = 0;
                send->s_queued = jiffies;
                send->s_op = NULL;

                nr_sig += rds_ib_set_wr_signal_state(ic, send, op->op_notify);

                send->s_wr.opcode = op->op_write ? IB_WR_RDMA_WRITE : IB_WR_RDMA_READ;
                send->s_rdma_wr.remote_addr = remote_addr;
                send->s_rdma_wr.rkey = op->op_rkey;

                if (num_sge > max_sge) {
                        send->s_rdma_wr.wr.num_sge = max_sge;
                        num_sge -= max_sge;
                } else {
                        send->s_rdma_wr.wr.num_sge = num_sge;
                }

                send->s_rdma_wr.wr.next = NULL;

                if (prev)
                        prev->s_rdma_wr.wr.next = &send->s_rdma_wr.wr;

                for (j = 0; j < send->s_rdma_wr.wr.num_sge &&
                     scat != &op->op_sg[op->op_count]; j++) {
                        len = ib_sg_dma_len(ic->i_cm_id->device, scat);
                        send->s_sge[j].addr =
                                 ib_sg_dma_address(ic->i_cm_id->device, scat);
                        send->s_sge[j].length = len;
                        send->s_sge[j].lkey = ic->i_pd->local_dma_lkey;

                        sent += len;
                        rdsdebug("ic %p sent %d remote_addr %llu\n", ic, sent, remote_addr);

                        remote_addr += len;
                        scat++;
                }

                rdsdebug("send %p wr %p num_sge %u next %p\n", send,
                        &send->s_rdma_wr.wr,
                        send->s_rdma_wr.wr.num_sge,
                        send->s_rdma_wr.wr.next);

                prev = send;
                if (++send == &ic->i_sends[ic->i_send_ring.w_nr])
                        send = ic->i_sends;
        }

        /* give a reference to the last op */
        if (scat == &op->op_sg[op->op_count]) {
                prev->s_op = op;
                rds_message_addref(container_of(op, struct rds_message, rdma));
        }

        if (i < work_alloc) {
                rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc - i);
                work_alloc = i;
        }

        if (nr_sig)
                atomic_add(nr_sig, &ic->i_signaled_sends);

        failed_wr = &first->s_rdma_wr.wr;
        ret = ib_post_send(ic->i_cm_id->qp, &first->s_rdma_wr.wr, &failed_wr);
        rdsdebug("ic %p first %p (wr %p) ret %d wr %p\n", ic,
                 first, &first->s_rdma_wr.wr, ret, failed_wr);
        BUG_ON(failed_wr != &first->s_rdma_wr.wr);
        if (ret) {
                printk(KERN_WARNING "RDS/IB: rdma ib_post_send to %pI4 "
                       "returned %d\n", &conn->c_faddr, ret);
                rds_ib_ring_unalloc(&ic->i_send_ring, work_alloc);
                rds_ib_sub_signaled(ic, nr_sig);
                goto out;
        }

        if (unlikely(failed_wr != &first->s_rdma_wr.wr)) {
                printk(KERN_WARNING "RDS/IB: ib_post_send() rc=%d, but failed_wqe updated!\n", ret);
                BUG_ON(failed_wr != &first->s_rdma_wr.wr);
        }


out:
        return ret;
}

void rds_ib_xmit_complete(struct rds_connection *conn)
{
        struct rds_ib_connection *ic = conn->c_transport_data;

        /* We may have a pending ACK or window update we were unable
         * to send previously (due to flow control). Try again. */
        rds_ib_attempt_ack(ic);
}