IB/srp: allow lockless work posting

Only one CPU at a time will own an RX IU, so using the address of the IU
as the work request cookie allows us to avoid taking a lock. We can
similarly prepare the TX path for lockless posting by moving the free TX
IUs to a list. This also removes the requirement that the queue sizes be
a power of 2.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
[ broken out, small cleanups, and modified to avoid needing an extra field
  in the IU by David Dillow]
Signed-off-by: David Dillow <dillowda@ornl.gov>

diff --git a/drivers/infiniband/ulp/srp/ib_srp.c b/drivers/infiniband/ulp/srp/ib_srp.c
index def9e6b..aa78d26 100644 (file)
--- a/drivers/infiniband/ulp/srp/ib_srp.c
+++ b/drivers/infiniband/ulp/srp/ib_srp.c
@@ -568,7 +568,7 @@ static int srp_reconnect_target(struct srp_target_port *target)
        struct ib_qp_attr qp_attr;
        struct srp_request *req, *tmp;
        struct ib_wc wc;
-       int ret;
+       int i, ret;
 
        if (!srp_change_state(target, SRP_TARGET_LIVE, SRP_TARGET_CONNECTING))
                return -EAGAIN;
@@ -601,9 +601,9 @@ static int srp_reconnect_target(struct srp_target_port *target)
                srp_reset_req(target, req);
        spin_unlock_irq(target->scsi_host->host_lock);
 
-       target->rx_head  = 0;
-       target->tx_head  = 0;
-       target->tx_tail  = 0;
+       list_del_init(&target->free_tx);
+       for (i = 0; i < SRP_SQ_SIZE; ++i)
+               list_move(&target->tx_ring[i]->list, &target->free_tx);
 
        target->qp_in_error = 0;
        ret = srp_connect_target(target);
@@ -817,7 +817,7 @@ static int srp_map_data(struct scsi_cmnd *scmnd, struct srp_target_port *target,
 
 /*
  * Must be called with target->scsi_host->host_lock held to protect
- * req_lim and tx_head.  Lock cannot be dropped between call here and
+ * req_lim and free_tx.  Lock cannot be dropped between call here and
  * call to __srp_post_send().
  *
  * Note:
@@ -837,7 +837,7 @@ static struct srp_iu *__srp_get_tx_iu(struct srp_target_port *target,
 
        srp_send_completion(target->send_cq, target);
 
-       if (target->tx_head - target->tx_tail >= SRP_SQ_SIZE)
+       if (list_empty(&target->free_tx))
                return NULL;
 
        /* Initiator responses to target requests do not consume credits */
@@ -846,14 +846,14 @@ static struct srp_iu *__srp_get_tx_iu(struct srp_target_port *target,
                return NULL;
        }
 
-       iu = target->tx_ring[target->tx_head & SRP_SQ_MASK];
+       iu = list_first_entry(&target->free_tx, struct srp_iu, list);
        iu->type = iu_type;
        return iu;
 }
 
 /*
  * Must be called with target->scsi_host->host_lock held to protect
- * req_lim and tx_head.
+ * req_lim and free_tx.
  */
 static int __srp_post_send(struct srp_target_port *target,
                           struct srp_iu *iu, int len)
@@ -867,7 +867,7 @@ static int __srp_post_send(struct srp_target_port *target,
        list.lkey   = target->srp_host->srp_dev->mr->lkey;
 
        wr.next       = NULL;
-       wr.wr_id      = target->tx_head & SRP_SQ_MASK;
+       wr.wr_id      = (uintptr_t) iu;
        wr.sg_list    = &list;
        wr.num_sge    = 1;
        wr.opcode     = IB_WR_SEND;
@@ -876,7 +876,7 @@ static int __srp_post_send(struct srp_target_port *target,
        ret = ib_post_send(target->qp, &wr, &bad_wr);
 
        if (!ret) {
-               ++target->tx_head;
+               list_del(&iu->list);
                if (iu->type != SRP_IU_RSP)
                        --target->req_lim;
        }
@@ -884,36 +884,21 @@ static int __srp_post_send(struct srp_target_port *target,
        return ret;
 }
 
-static int srp_post_recv(struct srp_target_port *target)
+static int srp_post_recv(struct srp_target_port *target, struct srp_iu *iu)
 {
-       unsigned long flags;
-       struct srp_iu *iu;
-       struct ib_sge list;
        struct ib_recv_wr wr, *bad_wr;
-       unsigned int next;
-       int ret;
-
-       spin_lock_irqsave(target->scsi_host->host_lock, flags);
-
-       next     = target->rx_head & SRP_RQ_MASK;
-       wr.wr_id = next;
-       iu       = target->rx_ring[next];
+       struct ib_sge list;
 
        list.addr   = iu->dma;
        list.length = iu->size;
        list.lkey   = target->srp_host->srp_dev->mr->lkey;
 
        wr.next     = NULL;
+       wr.wr_id    = (uintptr_t) iu;
        wr.sg_list  = &list;
        wr.num_sge  = 1;
 
-       ret = ib_post_recv(target->qp, &wr, &bad_wr);
-       if (!ret)
-               ++target->rx_head;
-
-       spin_unlock_irqrestore(target->scsi_host->host_lock, flags);
-
-       return ret;
+       return ib_post_recv(target->qp, &wr, &bad_wr);
 }
 
 static void srp_process_rsp(struct srp_target_port *target, struct srp_rsp *rsp)
@@ -1030,14 +1015,11 @@ static void srp_process_aer_req(struct srp_target_port *target,
 
 static void srp_handle_recv(struct srp_target_port *target, struct ib_wc *wc)
 {
-       struct ib_device *dev;
-       struct srp_iu *iu;
+       struct ib_device *dev = target->srp_host->srp_dev->dev;
+       struct srp_iu *iu = (struct srp_iu *) wc->wr_id;
        int res;
        u8 opcode;
 
-       iu = target->rx_ring[wc->wr_id];
-
-       dev = target->srp_host->srp_dev->dev;
        ib_dma_sync_single_for_cpu(dev, iu->dma, target->max_ti_iu_len,
                                   DMA_FROM_DEVICE);
 
@@ -1078,7 +1060,7 @@ static void srp_handle_recv(struct srp_target_port *target, struct ib_wc *wc)
        ib_dma_sync_single_for_device(dev, iu->dma, target->max_ti_iu_len,
                                      DMA_FROM_DEVICE);
 
-       res = srp_post_recv(target);
+       res = srp_post_recv(target, iu);
        if (res != 0)
                shost_printk(KERN_ERR, target->scsi_host,
                             PFX "Recv failed with error code %d\n", res);
@@ -1107,6 +1089,7 @@ static void srp_send_completion(struct ib_cq *cq, void *target_ptr)
 {
        struct srp_target_port *target = target_ptr;
        struct ib_wc wc;
+       struct srp_iu *iu;
 
        while (ib_poll_cq(cq, 1, &wc) > 0) {
                if (wc.status) {
@@ -1117,7 +1100,8 @@ static void srp_send_completion(struct ib_cq *cq, void *target_ptr)
                        break;
                }
 
-               ++target->tx_tail;
+               iu = (struct srp_iu *) wc.wr_id;
+               list_add(&iu->list, &target->free_tx);
        }
 }
 
@@ -1212,6 +1196,8 @@ static int srp_alloc_iu_bufs(struct srp_target_port *target)
                                                  GFP_KERNEL, DMA_TO_DEVICE);
                if (!target->tx_ring[i])
                        goto err;
+
+               list_add(&target->tx_ring[i]->list, &target->free_tx);
        }
 
        return 0;
@@ -1373,7 +1359,8 @@ static int srp_cm_handler(struct ib_cm_id *cm_id, struct ib_cm_event *event)
                        break;
 
                for (i = 0; i < SRP_RQ_SIZE; i++) {
-                       target->status = srp_post_recv(target);
+                       struct srp_iu *iu = target->rx_ring[i];
+                       target->status = srp_post_recv(target, iu);
                        if (target->status)
                                break;
                }
@@ -1965,6 +1952,7 @@ static ssize_t srp_create_target(struct device *dev,
        target->scsi_host  = target_host;
        target->srp_host   = host;
 
+       INIT_LIST_HEAD(&target->free_tx);
        INIT_LIST_HEAD(&target->free_reqs);
        INIT_LIST_HEAD(&target->req_queue);
        for (i = 0; i < SRP_CMD_SQ_SIZE; ++i) {
@@ -2235,8 +2223,7 @@ static int __init srp_init_module(void)
 {
        int ret;
 
-       BUILD_BUG_ON_NOT_POWER_OF_2(SRP_SQ_SIZE);
-       BUILD_BUG_ON_NOT_POWER_OF_2(SRP_RQ_SIZE);
+       BUILD_BUG_ON(FIELD_SIZEOF(struct ib_wc, wr_id) < sizeof(void *));
 
        if (srp_sg_tablesize > 255) {
                printk(KERN_WARNING PFX "Clamping srp_sg_tablesize to 255\n");

diff --git a/drivers/infiniband/ulp/srp/ib_srp.h b/drivers/infiniband/ulp/srp/ib_srp.h
index f8b689a..41ecb46 100644 (file)
--- a/drivers/infiniband/ulp/srp/ib_srp.h
+++ b/drivers/infiniband/ulp/srp/ib_srp.h
@@ -59,10 +59,8 @@ enum {
 
        SRP_RQ_SHIFT            = 6,
        SRP_RQ_SIZE             = 1 << SRP_RQ_SHIFT,
-       SRP_RQ_MASK             = SRP_RQ_SIZE - 1,
 
        SRP_SQ_SIZE             = SRP_RQ_SIZE,
-       SRP_SQ_MASK             = SRP_SQ_SIZE - 1,
        SRP_RSP_SQ_SIZE         = 1,
        SRP_REQ_SQ_SIZE         = SRP_SQ_SIZE - SRP_RSP_SQ_SIZE,
        SRP_TSK_MGMT_SQ_SIZE    = 1,
@@ -144,11 +142,9 @@ struct srp_target_port {
 
        int                     zero_req_lim;
 
-       unsigned                rx_head;
        struct srp_iu          *rx_ring[SRP_RQ_SIZE];
 
-       unsigned                tx_head;
-       unsigned                tx_tail;
+       struct list_head        free_tx;
        struct srp_iu          *tx_ring[SRP_SQ_SIZE];
 
        struct list_head        free_reqs;
@@ -168,6 +164,7 @@ struct srp_target_port {
 };
 
 struct srp_iu {
+       struct list_head        list;
        u64                     dma;
        void                   *buf;
        size_t                  size;