ib_isert: Add support for completion interrupt coalescing

This patch adds support for completion interrupt coalescing that
allows only every ISERT_COMP_BATCH_COUNT (8) to set IB_SEND_SIGNALED,
thus avoiding completion interrupts for every posted iser_tx_desc.

The batch processing is done using a per isert_conn llist that once
IB_SEND_SIGNALED has been set is saved to tx_desc->comp_llnode_batch,
and completion processing of previously posted iser_tx_descs is done
in a single shot from within isert_send_completion() code.

Note this is only done for response PDUs from ISCSI_OP_SCSI_CMD, and
all other control type of PDU responses will force an implicit batch
drain to occur.

Cc: Or Gerlitz <ogerlitz@mellanox.com>
Cc: Sagi Grimberg <sagig@mellanox.com>
Cc: Kent Overstreet <kmo@daterainc.com>
Cc: Roland Dreier <roland@purestorage.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/infiniband/ulp/isert/ib_isert.h b/drivers/infiniband/ulp/isert/ib_isert.h
index 631f209..691f90f 100644
--- a/drivers/infiniband/ulp/isert/ib_isert.h
+++ b/drivers/infiniband/ulp/isert/ib_isert.h
@@ -43,6 +43,8 @@ struct iser_tx_desc {
 	struct ib_sge	tx_sg[2];
 	int		num_sge;
 	struct isert_cmd *isert_cmd;
+	struct llist_node *comp_llnode_batch;
+	struct llist_node comp_llnode;
 	struct ib_send_wr send_wr;
 } __packed;
 
@@ -121,6 +123,10 @@ struct isert_conn {
 	int			conn_frwr_pool_size;
 	/* lock to protect frwr_pool */
 	spinlock_t		conn_lock;
+#define ISERT_COMP_BATCH_COUNT	8
+	int			conn_comp_batch;
+	struct llist_head	conn_comp_llist;
+	struct mutex		conn_comp_mutex;
 };
 
 #define ISERT_MAX_CQ 64