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ib_isert: Add support for completion interrupt coalescing
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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>
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Nicholas Bellinger committed Nov 6, 2013
1 parent 2dd1d53 commit 95b60f0
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Showing 2 changed files with 57 additions and 12 deletions.
63 changes: 51 additions & 12 deletions drivers/infiniband/ulp/isert/ib_isert.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@
#include <linux/socket.h>
#include <linux/in.h>
#include <linux/in6.h>
#include <linux/llist.h>
#include <rdma/ib_verbs.h>
#include <rdma/rdma_cm.h>
#include <target/target_core_base.h>
Expand Down Expand Up @@ -489,6 +490,7 @@ isert_connect_request(struct rdma_cm_id *cma_id, struct rdma_cm_event *event)
kref_init(&isert_conn->conn_kref);
kref_get(&isert_conn->conn_kref);
mutex_init(&isert_conn->conn_mutex);
mutex_init(&isert_conn->conn_comp_mutex);
spin_lock_init(&isert_conn->conn_lock);

cma_id->context = isert_conn;
Expand Down Expand Up @@ -843,14 +845,32 @@ isert_init_tx_hdrs(struct isert_conn *isert_conn,
}

static void
isert_init_send_wr(struct isert_cmd *isert_cmd, struct ib_send_wr *send_wr)
isert_init_send_wr(struct isert_conn *isert_conn, struct isert_cmd *isert_cmd,
struct ib_send_wr *send_wr, bool coalesce)
{
struct iser_tx_desc *tx_desc = &isert_cmd->tx_desc;

isert_cmd->rdma_wr.iser_ib_op = ISER_IB_SEND;
send_wr->wr_id = (unsigned long)&isert_cmd->tx_desc;
send_wr->opcode = IB_WR_SEND;
send_wr->send_flags = IB_SEND_SIGNALED;
send_wr->sg_list = &isert_cmd->tx_desc.tx_sg[0];
send_wr->sg_list = &tx_desc->tx_sg[0];
send_wr->num_sge = isert_cmd->tx_desc.num_sge;
/*
* Coalesce send completion interrupts by only setting IB_SEND_SIGNALED
* bit for every ISERT_COMP_BATCH_COUNT number of ib_post_send() calls.
*/
mutex_lock(&isert_conn->conn_comp_mutex);
if (coalesce &&
++isert_conn->conn_comp_batch < ISERT_COMP_BATCH_COUNT) {
llist_add(&tx_desc->comp_llnode, &isert_conn->conn_comp_llist);
mutex_unlock(&isert_conn->conn_comp_mutex);
return;
}
isert_conn->conn_comp_batch = 0;
tx_desc->comp_llnode_batch = llist_del_all(&isert_conn->conn_comp_llist);
mutex_unlock(&isert_conn->conn_comp_mutex);

send_wr->send_flags = IB_SEND_SIGNALED;
}

static int
Expand Down Expand Up @@ -1582,8 +1602,8 @@ isert_response_completion(struct iser_tx_desc *tx_desc,
}

static void
isert_send_completion(struct iser_tx_desc *tx_desc,
struct isert_conn *isert_conn)
__isert_send_completion(struct iser_tx_desc *tx_desc,
struct isert_conn *isert_conn)
{
struct ib_device *ib_dev = isert_conn->conn_cm_id->device;
struct isert_cmd *isert_cmd = tx_desc->isert_cmd;
Expand Down Expand Up @@ -1623,6 +1643,24 @@ isert_send_completion(struct iser_tx_desc *tx_desc,
}
}

static void
isert_send_completion(struct iser_tx_desc *tx_desc,
struct isert_conn *isert_conn)
{
struct llist_node *llnode = tx_desc->comp_llnode_batch;
struct iser_tx_desc *t;
/*
* Drain coalesced completion llist starting from comp_llnode_batch
* setup in isert_init_send_wr(), and then complete trailing tx_desc.
*/
while (llnode) {
t = llist_entry(llnode, struct iser_tx_desc, comp_llnode);
llnode = llist_next(llnode);
__isert_send_completion(t, isert_conn);
}
__isert_send_completion(tx_desc, isert_conn);
}

static void
isert_cq_comp_err(struct iser_tx_desc *tx_desc, struct isert_conn *isert_conn)
{
Expand Down Expand Up @@ -1793,7 +1831,7 @@ isert_put_response(struct iscsi_conn *conn, struct iscsi_cmd *cmd)
isert_cmd->tx_desc.num_sge = 2;
}

isert_init_send_wr(isert_cmd, send_wr);
isert_init_send_wr(isert_conn, isert_cmd, send_wr, true);

pr_debug("Posting SCSI Response IB_WR_SEND >>>>>>>>>>>>>>>>>>>>>>\n");

Expand All @@ -1813,7 +1851,7 @@ isert_put_nopin(struct iscsi_cmd *cmd, struct iscsi_conn *conn,
&isert_cmd->tx_desc.iscsi_header,
nopout_response);
isert_init_tx_hdrs(isert_conn, &isert_cmd->tx_desc);
isert_init_send_wr(isert_cmd, send_wr);
isert_init_send_wr(isert_conn, isert_cmd, send_wr, false);

pr_debug("Posting NOPIN Response IB_WR_SEND >>>>>>>>>>>>>>>>>>>>>>\n");

Expand All @@ -1831,7 +1869,7 @@ isert_put_logout_rsp(struct iscsi_cmd *cmd, struct iscsi_conn *conn)
iscsit_build_logout_rsp(cmd, conn, (struct iscsi_logout_rsp *)
&isert_cmd->tx_desc.iscsi_header);
isert_init_tx_hdrs(isert_conn, &isert_cmd->tx_desc);
isert_init_send_wr(isert_cmd, send_wr);
isert_init_send_wr(isert_conn, isert_cmd, send_wr, false);

pr_debug("Posting Logout Response IB_WR_SEND >>>>>>>>>>>>>>>>>>>>>>\n");

Expand All @@ -1849,7 +1887,7 @@ isert_put_tm_rsp(struct iscsi_cmd *cmd, struct iscsi_conn *conn)
iscsit_build_task_mgt_rsp(cmd, conn, (struct iscsi_tm_rsp *)
&isert_cmd->tx_desc.iscsi_header);
isert_init_tx_hdrs(isert_conn, &isert_cmd->tx_desc);
isert_init_send_wr(isert_cmd, send_wr);
isert_init_send_wr(isert_conn, isert_cmd, send_wr, false);

pr_debug("Posting Task Management Response IB_WR_SEND >>>>>>>>>>>>>>>>>>>>>>\n");

Expand Down Expand Up @@ -1881,7 +1919,7 @@ isert_put_reject(struct iscsi_cmd *cmd, struct iscsi_conn *conn)
tx_dsg->lkey = isert_conn->conn_mr->lkey;
isert_cmd->tx_desc.num_sge = 2;

isert_init_send_wr(isert_cmd, send_wr);
isert_init_send_wr(isert_conn, isert_cmd, send_wr, false);

pr_debug("Posting Reject IB_WR_SEND >>>>>>>>>>>>>>>>>>>>>>\n");

Expand Down Expand Up @@ -1921,7 +1959,7 @@ isert_put_text_rsp(struct iscsi_cmd *cmd, struct iscsi_conn *conn)
tx_dsg->lkey = isert_conn->conn_mr->lkey;
isert_cmd->tx_desc.num_sge = 2;
}
isert_init_send_wr(isert_cmd, send_wr);
isert_init_send_wr(isert_conn, isert_cmd, send_wr, false);

pr_debug("Posting Text Response IB_WR_SEND >>>>>>>>>>>>>>>>>>>>>>\n");

Expand Down Expand Up @@ -2309,7 +2347,8 @@ isert_put_datain(struct iscsi_conn *conn, struct iscsi_cmd *cmd)
iscsit_build_rsp_pdu(cmd, conn, false, (struct iscsi_scsi_rsp *)
&isert_cmd->tx_desc.iscsi_header);
isert_init_tx_hdrs(isert_conn, &isert_cmd->tx_desc);
isert_init_send_wr(isert_cmd, &isert_cmd->tx_desc.send_wr);
isert_init_send_wr(isert_conn, isert_cmd,
&isert_cmd->tx_desc.send_wr, true);

atomic_inc(&isert_conn->post_send_buf_count);

Expand Down
6 changes: 6 additions & 0 deletions drivers/infiniband/ulp/isert/ib_isert.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;

Expand Down Expand Up @@ -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
Expand Down

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