iser-target: Avoid using FRMR for single dma entry requests

This patch changes isert_reg_rdma_frwr() to not use FRMR for single
dma entry requests from small I/Os, in order to avoid the associated
memory registration overhead.

Using DMA MR is sufficient here for the single dma entry requests,
and addresses a >= v3.12 performance regression.

Signed-off-by: Vu Pham <vu@mellanox.com>
Cc: <stable@vger.kernel.org> # v3.12+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

diff --git a/drivers/infiniband/ulp/isert/ib_isert.c b/drivers/infiniband/ulp/isert/ib_isert.c
index 27708c3..bbd86e8 100644 (file)
--- a/drivers/infiniband/ulp/isert/ib_isert.c
+++ b/drivers/infiniband/ulp/isert/ib_isert.c
@@ -2297,18 +2297,26 @@ isert_reg_rdma_frwr(struct iscsi_conn *conn, struct iscsi_cmd *cmd,
        data_len = min(data_left, rdma_write_max);
        wr->cur_rdma_length = data_len;
 
-       spin_lock_irqsave(&isert_conn->conn_lock, flags);
-       fr_desc = list_first_entry(&isert_conn->conn_frwr_pool,
-                                  struct fast_reg_descriptor, list);
-       list_del(&fr_desc->list);
-       spin_unlock_irqrestore(&isert_conn->conn_lock, flags);
-       wr->fr_desc = fr_desc;
-
-       ret = isert_fast_reg_mr(fr_desc, isert_cmd, isert_conn,
-                         ib_sge, offset, data_len);
-       if (ret) {
-               list_add_tail(&fr_desc->list, &isert_conn->conn_frwr_pool);
-               goto unmap_sg;
+       /* if there is a single dma entry, dma mr is sufficient */
+       if (count == 1) {
+               ib_sge->addr = ib_sg_dma_address(ib_dev, &sg_start[0]);
+               ib_sge->length = ib_sg_dma_len(ib_dev, &sg_start[0]);
+               ib_sge->lkey = isert_conn->conn_mr->lkey;
+               wr->fr_desc = NULL;
+       } else {
+               spin_lock_irqsave(&isert_conn->conn_lock, flags);
+               fr_desc = list_first_entry(&isert_conn->conn_frwr_pool,
+                                          struct fast_reg_descriptor, list);
+               list_del(&fr_desc->list);
+               spin_unlock_irqrestore(&isert_conn->conn_lock, flags);
+               wr->fr_desc = fr_desc;
+
+               ret = isert_fast_reg_mr(fr_desc, isert_cmd, isert_conn,
+                                 ib_sge, offset, data_len);
+               if (ret) {
+                       list_add_tail(&fr_desc->list, &isert_conn->conn_frwr_pool);
+                       goto unmap_sg;
+               }
        }
 
        return 0;