On 9/19/2014 4:00 PM, Bart Van Assche wrote:
Improve performance by using multiple RDMA/RC channels per SCSI host
for communicating with an SRP target.


Hey Bart,

Since you don't seem to negotiate/declare multichannel with the target,
did you test this code with some target implementations other than SCST
that happen to be out there?

Overall, I think this patch would be easier to review if you also provide a list of logical changes (which obviously are introduced in this patch). Patch 7/8 can use some more information of target-channel
relations as well.

Signed-off-by: Bart Van Assche <bvanass...@acm.org>
---
  Documentation/ABI/stable/sysfs-driver-ib_srp |  25 +-
  drivers/infiniband/ulp/srp/ib_srp.c          | 337 ++++++++++++++++++++-------
  drivers/infiniband/ulp/srp/ib_srp.h          |  20 +-
  3 files changed, 287 insertions(+), 95 deletions(-)

diff --git a/Documentation/ABI/stable/sysfs-driver-ib_srp 
b/Documentation/ABI/stable/sysfs-driver-ib_srp
index b9688de..d5a459e 100644
--- a/Documentation/ABI/stable/sysfs-driver-ib_srp
+++ b/Documentation/ABI/stable/sysfs-driver-ib_srp
@@ -55,12 +55,12 @@ Description:        Interface for making ib_srp connect to 
a new target.
                  only safe with partial memory descriptor list support enabled
                  (allow_ext_sg=1).
                * comp_vector, a number in the range 0..n-1 specifying the
-                 MSI-X completion vector. Some HCA's allocate multiple (n)
-                 MSI-X vectors per HCA port. If the IRQ affinity masks of
-                 these interrupts have been configured such that each MSI-X
-                 interrupt is handled by a different CPU then the comp_vector
-                 parameter can be used to spread the SRP completion workload
-                 over multiple CPU's.
+                 MSI-X completion vector of the first RDMA channel. Some
+                 HCA's allocate multiple (n) MSI-X vectors per HCA port. If
+                 the IRQ affinity masks of these interrupts have been
+                 configured such that each MSI-X interrupt is handled by a
+                 different CPU then the comp_vector parameter can be used to
+                 spread the SRP completion workload over multiple CPU's.


Why do you want the first channel vector placement? Why can't you start
with obvious 0?


                * tl_retry_count, a number in the range 2..7 specifying the
                  IB RC retry count.
                * queue_size, the maximum number of commands that the
@@ -88,6 +88,13 @@ Description: Whether ib_srp is allowed to include a partial 
memory
                descriptor list in an SRP_CMD when communicating with an SRP
                target.

+What:          /sys/class/scsi_host/host<n>/ch_count
+Date:          November 1, 2014
+KernelVersion: 3.18
+Contact:       linux-r...@vger.kernel.org
+Description:   Number of RDMA channels used for communication with the SRP
+               target.
+
  What:         /sys/class/scsi_host/host<n>/cmd_sg_entries
  Date:         May 19, 2011
  KernelVersion:        2.6.39
@@ -95,6 +102,12 @@ Contact:    linux-r...@vger.kernel.org
  Description:  Maximum number of data buffer descriptors that may be sent to
                the target in a single SRP_CMD request.

+What:          /sys/class/scsi_host/host<n>/comp_vector
+Date:          September 2, 2013
+KernelVersion: 3.11
+Contact:       linux-r...@vger.kernel.org
+Description:   Completion vector used for the first RDMA channel.
+
  What:         /sys/class/scsi_host/host<n>/dgid
  Date:         June 17, 2006
  KernelVersion:        2.6.17
diff --git a/drivers/infiniband/ulp/srp/ib_srp.c 
b/drivers/infiniband/ulp/srp/ib_srp.c
index 9feeea1..58ca618 100644
--- a/drivers/infiniband/ulp/srp/ib_srp.c
+++ b/drivers/infiniband/ulp/srp/ib_srp.c
@@ -123,6 +123,16 @@ MODULE_PARM_DESC(dev_loss_tmo,
                 " if fast_io_fail_tmo has not been set. \"off\" means that"
                 " this functionality is disabled.");

+static unsigned ch_count;
+module_param(ch_count, uint, 0444);
+MODULE_PARM_DESC(ch_count,
+                "Number of RDMA channels to use for communication with an SRP"
+                " target. Using more than one channel improves performance"
+                " if the HCA supports multiple completion vectors. The"
+                " default value is the minimum of four times the number of"
+                " online CPU sockets and the number of completion vectors"
+                " supported by the HCA.");
+

Can you explain the default math? how did you end-up with 4*numa_nodes?
wouldn't per-cpu be a better fit?

Moreover, while using multiple channels you don't suffice for less
requests of less FMRs/FRs. I'm a bit concerned here about scalability
of multi-channel.

Should we take care of cases where the user will want lots of channels
to lots of targets and might run out of resources?

  static void srp_add_one(struct ib_device *device);
  static void srp_remove_one(struct ib_device *device);
  static void srp_recv_completion(struct ib_cq *cq, void *ch_ptr);
@@ -556,17 +566,32 @@ err:
   * Note: this function may be called without srp_alloc_iu_bufs() having been
   * invoked. Hence the ch->[rt]x_ring checks.
   */
-static void srp_free_ch_ib(struct srp_rdma_ch *ch)
+static void srp_free_ch_ib(struct srp_target_port *target,
+                          struct srp_rdma_ch *ch)
  {
-       struct srp_target_port *target = ch->target;
        struct srp_device *dev = target->srp_host->srp_dev;
        int i;

+       if (!ch->target)
+               return;

How did this condition pop up here? As I don't feel this is a trivial
condition, I would like to see a comment of how can this routine be called twice and why is this peek safe?

+
+       /*
+        * Avoid that the SCSI error handler tries to use this channel after
+        * it has been freed. The SCSI error handler can namely continue
+        * trying to perform recovery actions after scsi_remove_host()
+        * returned.
+        */
+       ch->target = NULL;
+
        if (ch->cm_id) {
                ib_destroy_cm_id(ch->cm_id);
                ch->cm_id = NULL;
        }

+       /* If srp_new_cm_id() succeeded but srp_create_ch_ib() not, return. */
+       if (!ch->qp)
+               return;
+
        if (dev->use_fast_reg) {
                if (ch->fr_pool)
                        srp_destroy_fr_pool(ch->fr_pool);
@@ -647,7 +672,7 @@ static int srp_lookup_path(struct srp_rdma_ch *ch)
        return ch->status;
  }

-static int srp_send_req(struct srp_rdma_ch *ch)
+static int srp_send_req(struct srp_rdma_ch *ch, bool multich)
  {
        struct srp_target_port *target = ch->target;
        struct {
@@ -688,6 +713,8 @@ static int srp_send_req(struct srp_rdma_ch *ch)
        req->priv.req_it_iu_len = cpu_to_be32(target->max_iu_len);
        req->priv.req_buf_fmt        = cpu_to_be16(SRP_BUF_FORMAT_DIRECT |
                                              SRP_BUF_FORMAT_INDIRECT);
+       req->priv.req_flags  = (multich ? SRP_MULTICHAN_MULTI :
+                                  SRP_MULTICHAN_SINGLE);
        /*
         * In the published SRP specification (draft rev. 16a), the
         * port identifier format is 8 bytes of ID extension followed
@@ -769,27 +796,31 @@ static bool srp_change_conn_state(struct srp_target_port 
*target,

  static void srp_disconnect_target(struct srp_target_port *target)
  {
-       struct srp_rdma_ch *ch = &target->ch;
+       struct srp_rdma_ch *ch;
+       int i;

        if (srp_change_conn_state(target, false)) {
                /* XXX should send SRP_I_LOGOUT request */

-               if (ib_send_cm_dreq(ch->cm_id, NULL, 0)) {
-                       shost_printk(KERN_DEBUG, target->scsi_host,
-                                    PFX "Sending CM DREQ failed\n");
+               for (i = 0; i < target->ch_count; i++) {
+                       ch = &target->ch[i];
+                       if (ch->cm_id && ib_send_cm_dreq(ch->cm_id, NULL, 0)) {
+                               shost_printk(KERN_DEBUG, target->scsi_host,
+                                            PFX "Sending CM DREQ failed\n");
+                       }
                }
        }
  }

-static void srp_free_req_data(struct srp_rdma_ch *ch)
+static void srp_free_req_data(struct srp_target_port *target,
+                             struct srp_rdma_ch *ch)
  {
-       struct srp_target_port *target = ch->target;
        struct srp_device *dev = target->srp_host->srp_dev;
        struct ib_device *ibdev = dev->dev;
        struct srp_request *req;
        int i;

-       if (!ch->req_ring)
+       if (!ch->target || !ch->req_ring)
                return;

        for (i = 0; i < target->req_ring_size; ++i) {
@@ -853,7 +884,7 @@ static int srp_alloc_req_data(struct srp_rdma_ch *ch)
                        goto out;

                req->indirect_dma_addr = dma_addr;
-               req->index = i;
+               req->tag = build_srp_tag(ch - target->ch, i);
                list_add_tail(&req->list, &ch->free_reqs);
        }
        ret = 0;
@@ -879,7 +910,8 @@ static void srp_del_scsi_host_attr(struct Scsi_Host *shost)

  static void srp_remove_target(struct srp_target_port *target)
  {
-       struct srp_rdma_ch *ch = &target->ch;
+       struct srp_rdma_ch *ch;
+       int i;

        WARN_ON_ONCE(target->state != SRP_TARGET_REMOVED);

@@ -889,10 +921,18 @@ static void srp_remove_target(struct srp_target_port 
*target)
        scsi_remove_host(target->scsi_host);
        srp_stop_rport_timers(target->rport);
        srp_disconnect_target(target);
-       srp_free_ch_ib(ch);
+       for (i = 0; i < target->ch_count; i++) {
+               ch = &target->ch[i];
+               srp_free_ch_ib(target, ch);
+       }
        cancel_work_sync(&target->tl_err_work);
        srp_rport_put(target->rport);
-       srp_free_req_data(ch);
+       for (i = 0; i < target->ch_count; i++) {
+               ch = &target->ch[i];
+               srp_free_req_data(target, ch);
+       }
+       kfree(target->ch);
+       target->ch = NULL;

        spin_lock(&target->srp_host->target_lock);
        list_del(&target->list);
@@ -918,12 +958,12 @@ static void srp_rport_delete(struct srp_rport *rport)
        srp_queue_remove_work(target);
  }

-static int srp_connect_ch(struct srp_rdma_ch *ch)
+static int srp_connect_ch(struct srp_rdma_ch *ch, bool multich)
  {
        struct srp_target_port *target = ch->target;
        int ret;

-       WARN_ON_ONCE(target->connected);
+       WARN_ON_ONCE(!multich && target->connected);

        target->qp_in_error = false;

@@ -933,7 +973,7 @@ static int srp_connect_ch(struct srp_rdma_ch *ch)

        while (1) {
                init_completion(&ch->done);
-               ret = srp_send_req(ch);
+               ret = srp_send_req(ch, multich);
                if (ret)
                        return ret;
                ret = wait_for_completion_interruptible(&ch->done);
@@ -1095,10 +1135,10 @@ static void srp_finish_req(struct srp_rdma_ch *ch, 
struct srp_request *req,
  static void srp_terminate_io(struct srp_rport *rport)
  {
        struct srp_target_port *target = rport->lld_data;
-       struct srp_rdma_ch *ch = &target->ch;
+       struct srp_rdma_ch *ch;
        struct Scsi_Host *shost = target->scsi_host;
        struct scsi_device *sdev;
-       int i;
+       int i, j;

        /*
         * Invoking srp_terminate_io() while srp_queuecommand() is running
@@ -1107,10 +1147,15 @@ static void srp_terminate_io(struct srp_rport *rport)
        shost_for_each_device(sdev, shost)
                WARN_ON_ONCE(sdev->request_queue->request_fn_active);

-       for (i = 0; i < target->req_ring_size; ++i) {
-               struct srp_request *req = &ch->req_ring[i];
+       for (i = 0; i < target->ch_count; i++) {
+               ch = &target->ch[i];
+
+               for (j = 0; j < target->req_ring_size; ++j) {
+                       struct srp_request *req = &ch->req_ring[j];

-               srp_finish_req(ch, req, NULL, DID_TRANSPORT_FAILFAST << 16);
+                       srp_finish_req(ch, req, NULL,
+                                      DID_TRANSPORT_FAILFAST << 16);
+               }
        }
  }

@@ -1126,8 +1171,9 @@ static void srp_terminate_io(struct srp_rport *rport)
  static int srp_rport_reconnect(struct srp_rport *rport)
  {
        struct srp_target_port *target = rport->lld_data;
-       struct srp_rdma_ch *ch = &target->ch;
-       int i, ret;
+       struct srp_rdma_ch *ch;
+       int i, j, ret = 0;
+       bool multich = false;

        srp_disconnect_target(target);

@@ -1139,27 +1185,43 @@ static int srp_rport_reconnect(struct srp_rport *rport)
         * case things are really fouled up. Doing so also ensures that all CM
         * callbacks will have finished before a new QP is allocated.
         */
-       ret = srp_new_cm_id(ch);
-
-       for (i = 0; i < target->req_ring_size; ++i) {
-               struct srp_request *req = &ch->req_ring[i];
-
-               srp_finish_req(ch, req, NULL, DID_RESET << 16);
+       for (i = 0; i < target->ch_count; i++) {
+               ch = &target->ch[i];
+               if (!ch->target)
+                       return -ENODEV;
+               ret += srp_new_cm_id(ch);
+       }
+       for (i = 0; i < target->ch_count; i++) {
+               ch = &target->ch[i];
+               for (j = 0; j < target->req_ring_size; ++j) {
+                       struct srp_request *req = &ch->req_ring[j];
+
+                       srp_finish_req(ch, req, NULL, DID_RESET << 16);
+               }
        }
+       for (i = 0; i < target->ch_count; i++) {
+               ch = &target->ch[i];
+               /*
+                * Whether or not creating a new CM ID succeeded, create a new
+                * QP. This guarantees that all completion callback function
+                * invocations have finished before request resetting starts.
+                */
+               ret += srp_create_ch_ib(ch);

-       /*
-        * Whether or not creating a new CM ID succeeded, create a new
-        * QP. This guarantees that all callback functions for the old QP have
-        * finished before any send requests are posted on the new QP.
-        */
-       ret += srp_create_ch_ib(ch);
-
-       INIT_LIST_HEAD(&ch->free_tx);
-       for (i = 0; i < target->queue_size; ++i)
-               list_add(&ch->tx_ring[i]->list, &ch->free_tx);
-
-       if (ret == 0)
-               ret = srp_connect_ch(ch);
+               INIT_LIST_HEAD(&ch->free_tx);
+               for (j = 0; j < target->queue_size; ++j)
+                       list_add(&ch->tx_ring[j]->list, &ch->free_tx);
+       }
+       for (i = 0; i < target->ch_count; i++) {
+               ch = &target->ch[i];
+               if (ret) {
+                       if (i > 1)
+                               ret = 0;
+                       break;
+               }
+               ret = srp_connect_ch(ch, multich);
+               multich = true;
+       }

        if (ret == 0)
                shost_printk(KERN_INFO, target->scsi_host,
@@ -1573,7 +1635,7 @@ static struct srp_iu *__srp_get_tx_iu(struct srp_rdma_ch 
*ch,
        s32 rsv = (iu_type == SRP_IU_TSK_MGMT) ? 0 : SRP_TSK_MGMT_SQ_SIZE;
        struct srp_iu *iu;

-       srp_send_completion(ch->send_cq, target);
+       srp_send_completion(ch->send_cq, ch);

        if (list_empty(&ch->free_tx))
                return NULL;
@@ -1637,6 +1699,7 @@ static void srp_process_rsp(struct srp_rdma_ch *ch, 
struct srp_rsp *rsp)
        struct srp_request *req;
        struct scsi_cmnd *scmnd;
        unsigned long flags;
+       unsigned i;

        if (unlikely(rsp->tag & SRP_TAG_TSK_MGMT)) {
                spin_lock_irqsave(&ch->lock, flags);
@@ -1648,12 +1711,20 @@ static void srp_process_rsp(struct srp_rdma_ch *ch, 
struct srp_rsp *rsp)
                        ch->tsk_mgmt_status = rsp->data[3];
                complete(&ch->tsk_mgmt_done);
        } else {
-               req = &ch->req_ring[rsp->tag];
-               scmnd = srp_claim_req(ch, req, NULL, NULL);
+               if (srp_tag_ch(rsp->tag) != ch - target->ch)
+                       pr_err("Channel idx mismatch: tag %#llx <> ch %#lx\n",
+                              rsp->tag, ch - target->ch);
+               i = srp_tag_idx(rsp->tag);
+               if (i < target->req_ring_size) {
+                       req = &ch->req_ring[i];
+                       scmnd = srp_claim_req(ch, req, NULL, NULL);
+               } else {
+                       scmnd = NULL;
+               }
                if (!scmnd) {
                        shost_printk(KERN_ERR, target->scsi_host,
-                                    "Null scmnd for RSP w/tag %016llx\n",
-                                    (unsigned long long) rsp->tag);
+                                    "Null scmnd for RSP w/tag %#016llx received on 
ch %ld / QP %#x\n",
+                                    rsp->tag, ch - target->ch, ch->qp->qp_num);

                        spin_lock_irqsave(&ch->lock, flags);
                        ch->req_lim += be32_to_cpu(rsp->req_lim_delta);
@@ -1879,7 +1950,8 @@ static void srp_send_completion(struct ib_cq *cq, void 
*ch_ptr)
        }
  }

-static int srp_queuecommand(struct Scsi_Host *shost, struct scsi_cmnd *scmnd)
+static int srp_queuecommand(unsigned hwq, struct Scsi_Host *shost,
+                           struct scsi_cmnd *scmnd)
  {
        struct srp_target_port *target = host_to_target(shost);
        struct srp_rport *rport = target->rport;
@@ -1905,7 +1977,7 @@ static int srp_queuecommand(struct Scsi_Host *shost, 
struct scsi_cmnd *scmnd)
        if (unlikely(scmnd->result))
                goto err;

-       ch = &target->ch;
+       ch = &target->ch[hwq];

        spin_lock_irqsave(&ch->lock, flags);
        iu = __srp_get_tx_iu(ch, SRP_IU_CMD);
@@ -1927,7 +1999,7 @@ static int srp_queuecommand(struct Scsi_Host *shost, 
struct scsi_cmnd *scmnd)

        cmd->opcode = SRP_CMD;
        cmd->lun    = cpu_to_be64((u64) scmnd->device->lun << 48);
-       cmd->tag    = req->index;
+       cmd->tag    = req->tag;
        memcpy(cmd->cdb, scmnd->cmnd, scmnd->cmd_len);

        req->scmnd    = scmnd;
@@ -1993,6 +2065,17 @@ err:
        goto unlock_rport;
  }

+static int srp_sq_queuecommand(struct Scsi_Host *shost, struct scsi_cmnd 
*scmnd)
+{
+       return srp_queuecommand(0, shost, scmnd);
+}
+
+static int srp_mq_queuecommand(struct blk_mq_hw_ctx *hctx,
+                              struct scsi_cmnd *scmnd)
+{
+       return srp_queuecommand(hctx->queue_num, scmnd->device->host, scmnd);
+}
+
  /*
   * Note: the resources allocated in this function are freed in
   * srp_free_ch_ib().
@@ -2409,15 +2492,23 @@ static int srp_abort(struct scsi_cmnd *scmnd)
  {
        struct srp_target_port *target = host_to_target(scmnd->device->host);
        struct srp_request *req = (struct srp_request *) scmnd->host_scribble;
+       u16 ch_idx;
        struct srp_rdma_ch *ch;
        int ret;

        shost_printk(KERN_ERR, target->scsi_host, "SRP abort called\n");

-       ch = &target->ch;
-       if (!req || !srp_claim_req(ch, req, NULL, scmnd))
+       if (!req)
+               return SUCCESS;
+       ch_idx = srp_tag_ch(req->tag);
+       if (WARN_ON_ONCE(ch_idx >= target->ch_count))

Can you explain how can this happen? and why do you continue as if
nothing happened?

                return SUCCESS;
-       if (srp_send_tsk_mgmt(ch, req->index, scmnd->device->lun,
+       ch = &target->ch[ch_idx];
+       if (!srp_claim_req(ch, req, NULL, scmnd))
+               return SUCCESS;
+       shost_printk(KERN_ERR, target->scsi_host,
+                    "Sending SRP abort for tag %#x\n", req->tag);
+       if (srp_send_tsk_mgmt(ch, req->tag, scmnd->device->lun,
                              SRP_TSK_ABORT_TASK) == 0)
                ret = SUCCESS;
        else if (target->rport->state == SRP_RPORT_LOST)
@@ -2434,21 +2525,25 @@ static int srp_abort(struct scsi_cmnd *scmnd)
  static int srp_reset_device(struct scsi_cmnd *scmnd)
  {
        struct srp_target_port *target = host_to_target(scmnd->device->host);
-       struct srp_rdma_ch *ch = &target->ch;
+       struct srp_rdma_ch *ch;
        int i;

        shost_printk(KERN_ERR, target->scsi_host, "SRP reset_device called\n");

+       ch = &target->ch[0];
        if (srp_send_tsk_mgmt(ch, SRP_TAG_NO_REQ, scmnd->device->lun,
                              SRP_TSK_LUN_RESET))
                return FAILED;
        if (ch->tsk_mgmt_status)
                return FAILED;

-       for (i = 0; i < target->req_ring_size; ++i) {
-               struct srp_request *req = &ch->req_ring[i];
+       for (i = 0; i < target->ch_count; i++) {

Just a Nit, This channels loop appears several times in the code.
Might be nicer to macro it to for_each_rdma_ch() - not a must though...

+               ch = &target->ch[i];
+               for (i = 0; i < target->req_ring_size; ++i) {
+                       struct srp_request *req = &ch->req_ring[i];

-               srp_finish_req(ch, req, scmnd->device, DID_RESET << 16);
+                       srp_finish_req(ch, req, scmnd->device, DID_RESET << 16);
+               }
        }

        return SUCCESS;
@@ -2525,7 +2620,7 @@ static ssize_t show_dgid(struct device *dev, struct 
device_attribute *attr,
                         char *buf)
  {
        struct srp_target_port *target = host_to_target(class_to_shost(dev));
-       struct srp_rdma_ch *ch = &target->ch;
+       struct srp_rdma_ch *ch = &target->ch[0];

        return sprintf(buf, "%pI6\n", ch->path.dgid.raw);
  }
@@ -2542,8 +2637,14 @@ static ssize_t show_req_lim(struct device *dev,
                            struct device_attribute *attr, char *buf)
  {
        struct srp_target_port *target = host_to_target(class_to_shost(dev));
+       struct srp_rdma_ch *ch;
+       int i, req_lim = INT_MAX;

-       return sprintf(buf, "%d\n", target->ch.req_lim);
+       for (i = 0; i < target->ch_count; i++) {
+               ch = &target->ch[i];

No lock here?

+               req_lim = min(req_lim, ch->req_lim);
+       }
+       return sprintf(buf, "%d\n", req_lim);
  }

  static ssize_t show_zero_req_lim(struct device *dev,
@@ -2570,6 +2671,14 @@ static ssize_t show_local_ib_device(struct device *dev,
        return sprintf(buf, "%s\n", target->srp_host->srp_dev->dev->name);
  }

+static ssize_t show_ch_count(struct device *dev, struct device_attribute *attr,
+                            char *buf)
+{
+       struct srp_target_port *target = host_to_target(class_to_shost(dev));
+
+       return sprintf(buf, "%d\n", target->ch_count);
+}
+
  static ssize_t show_comp_vector(struct device *dev,
                                struct device_attribute *attr, char *buf)
  {
@@ -2613,6 +2722,7 @@ static DEVICE_ATTR(req_lim,         S_IRUGO, 
show_req_lim,         NULL);
  static DEVICE_ATTR(zero_req_lim,    S_IRUGO, show_zero_req_lim,          
NULL);
  static DEVICE_ATTR(local_ib_port,   S_IRUGO, show_local_ib_port,   NULL);
  static DEVICE_ATTR(local_ib_device, S_IRUGO, show_local_ib_device, NULL);
+static DEVICE_ATTR(ch_count,        S_IRUGO, show_ch_count,        NULL);
  static DEVICE_ATTR(comp_vector,     S_IRUGO, show_comp_vector,     NULL);
  static DEVICE_ATTR(tl_retry_count,  S_IRUGO, show_tl_retry_count,  NULL);
  static DEVICE_ATTR(cmd_sg_entries,  S_IRUGO, show_cmd_sg_entries,  NULL);
@@ -2630,6 +2740,7 @@ static struct device_attribute *srp_host_attrs[] = {
        &dev_attr_zero_req_lim,
        &dev_attr_local_ib_port,
        &dev_attr_local_ib_device,
+       &dev_attr_ch_count,
        &dev_attr_comp_vector,
        &dev_attr_tl_retry_count,
        &dev_attr_cmd_sg_entries,
@@ -2643,7 +2754,8 @@ static struct scsi_host_template srp_template = {
        .proc_name                      = DRV_NAME,
        .slave_configure                = srp_slave_configure,
        .info                           = srp_target_info,
-       .queuecommand                   = srp_queuecommand,
+       .queuecommand                   = srp_sq_queuecommand,
+       .mq_queuecommand                = srp_mq_queuecommand,
        .change_queue_depth             = srp_change_queue_depth,
        .change_queue_type              = srp_change_queue_type,
        .eh_abort_handler               = srp_abort,
@@ -3038,7 +3150,8 @@ static ssize_t srp_create_target(struct device *dev,
        struct srp_rdma_ch *ch;
        struct srp_device *srp_dev = host->srp_dev;
        struct ib_device *ibdev = srp_dev->dev;
-       int ret;
+       int ret, node_idx, node, cpu, i;
+       bool multich = false;

        target_host = scsi_host_alloc(&srp_template,
                                      sizeof (struct srp_target_port));
@@ -3098,34 +3211,82 @@ static ssize_t srp_create_target(struct device *dev,
        INIT_WORK(&target->tl_err_work, srp_tl_err_work);
        INIT_WORK(&target->remove_work, srp_remove_work);
        spin_lock_init(&target->lock);
-       ch = &target->ch;
-       ch->target = target;
-       ch->comp_vector = target->comp_vector;
-       spin_lock_init(&ch->lock);
-       INIT_LIST_HEAD(&ch->free_tx);
-       ret = srp_alloc_req_data(ch);
-       if (ret)
-               goto err_free_mem;
-
        ret = ib_query_gid(ibdev, host->port, 0, &target->sgid);
        if (ret)
-               goto err_free_mem;
+               goto err;

-       ret = srp_create_ch_ib(ch);
-       if (ret)
-               goto err_free_mem;
+       ret = -ENOMEM;

Any chance you take this non-trivial setup below to a routine and
document what you are trying to attempt?

+       target->ch_count = max_t(unsigned, num_online_nodes(),
+                                min(ch_count ? :
+                                    min(4 * num_online_nodes(),
+                                        ibdev->num_comp_vectors),
+                                    num_online_cpus()));
+       target->ch = kcalloc(target->ch_count, sizeof(*target->ch),
+                            GFP_KERNEL);
+       if (!target->ch)
+               goto err;

-       ret = srp_new_cm_id(ch);
-       if (ret)
-               goto err_free_ib;
+       node_idx = 0;
+       for_each_online_node(node) {
+               const int ch_start = (node_idx * target->ch_count /
+                                     num_online_nodes());
+               const int ch_end = ((node_idx + 1) * target->ch_count /
+                                   num_online_nodes());
+               const int cv_start = (node_idx * ibdev->num_comp_vectors /
+                                     num_online_nodes() + target->comp_vector)
+                                    % ibdev->num_comp_vectors;
+               const int cv_end = ((node_idx + 1) * ibdev->num_comp_vectors /
+                                   num_online_nodes() + target->comp_vector)
+                                  % ibdev->num_comp_vectors;
+               int cpu_idx = 0;
+
+               for_each_online_cpu(cpu) {
+                       if (cpu_to_node(cpu) != node)
+                               continue;
+                       if (ch_start + cpu_idx >= ch_end)
+                               continue;
+                       ch = &target->ch[ch_start + cpu_idx];
+                       ch->target = target;
+                       ch->comp_vector = cv_start == cv_end ? cv_start :
+                               cv_start + cpu_idx % (cv_end - cv_start);
+                       spin_lock_init(&ch->lock);
+                       INIT_LIST_HEAD(&ch->free_tx);
+                       ret = srp_new_cm_id(ch);
+                       if (ret)
+                               goto err_disconnect;

-       ret = srp_connect_ch(ch);
-       if (ret) {
-               shost_printk(KERN_ERR, target->scsi_host,
-                            PFX "Connection failed\n");
-               goto err_free_ib;
+                       ret = srp_create_ch_ib(ch);
+                       if (ret)
+                               goto err_disconnect;
+
+                       ret = srp_alloc_req_data(ch);
+                       if (ret)
+                               goto err_disconnect;
+
+                       ret = srp_connect_ch(ch, multich);
+                       if (ret) {
+                               shost_printk(KERN_ERR, target->scsi_host,
+                                            PFX "Connection %d/%d failed\n",
+                                            ch_start + cpu_idx,
+                                            target->ch_count);
+                               if (node_idx == 0 && cpu_idx == 0) {
+                                       goto err_disconnect;
+                               } else {
+                                       srp_free_ch_ib(target, ch);
+                                       srp_free_req_data(target, ch);
+                                       target->ch_count = ch - target->ch;
+                                       break;
+                               }
+                       }
+
+                       multich = true;
+                       cpu_idx++;
+               }
+               node_idx++;
        }

+       target->scsi_host->nr_hw_queues = target->ch_count;
+
        ret = srp_add_target(host, target);
        if (ret)
                goto err_disconnect;
@@ -3154,11 +3315,13 @@ out:
  err_disconnect:
        srp_disconnect_target(target);

-err_free_ib:
-       srp_free_ch_ib(ch);
+       for (i = 0; i < target->ch_count; i++) {
+               ch = &target->ch[i];
+               srp_free_ch_ib(target, ch);
+               srp_free_req_data(target, ch);
+       }

-err_free_mem:
-       srp_free_req_data(ch);
+       kfree(target->ch);

  err:
        scsi_host_put(target_host);
diff --git a/drivers/infiniband/ulp/srp/ib_srp.h 
b/drivers/infiniband/ulp/srp/ib_srp.h
index 0609124..d9660e1 100644
--- a/drivers/infiniband/ulp/srp/ib_srp.h
+++ b/drivers/infiniband/ulp/srp/ib_srp.h
@@ -84,6 +84,21 @@ enum srp_iu_type {
        SRP_IU_RSP,
  };

+static inline u32 build_srp_tag(u16 ch, u16 req_idx)
+{
+       return ch << 16 | req_idx;
+}
+
+static inline u16 srp_tag_ch(u32 tag)
+{
+       return tag >> 16;
+}
+
+static inline u16 srp_tag_idx(u32 tag)
+{
+       return tag & ((1 << 16) - 1);
+}
+
  /*
   * @mr_page_mask: HCA memory registration page mask.
   * @mr_page_size: HCA memory registration page size.
@@ -127,7 +142,7 @@ struct srp_request {
        struct srp_direct_buf  *indirect_desc;
        dma_addr_t              indirect_dma_addr;
        short                   nmdesc;
-       short                   index;
+       uint32_t                tag;
  };

  struct srp_rdma_ch {
@@ -173,8 +188,9 @@ struct srp_target_port {
        /* read and written in the hot path */
        spinlock_t              lock;

-       struct srp_rdma_ch      ch;
        /* read only in the hot path */
+       struct srp_rdma_ch      *ch;
+       u32                     ch_count;
        u32                     lkey;
        u32                     rkey;
        enum srp_target_state   state;


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