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Commit 9fd60088 authored by Jenny Derzhavetz's avatar Jenny Derzhavetz Committed by Nicholas Bellinger
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iser-target: Skip data copy if all the command data comes as immediate 



Given that supporting zcopy immediate data for all IOs requires
iser driver to use its own buffer allocations, we settle with
avoiding data copy for IOs with data length of up to 8K (which
is more latency sensitive anyway).

This trims IO write latency by up to 3us and increase IOPs
by up to 40% by saving CPU time doing sg_copy_from_buffer
(8K IO size is the obvious winner here).

Signed-off-by: default avatarJenny Derzhavetz <jennyf@mellanox.com>
Signed-off-by: default avatarSagi Grimberg <sagig@mellanox.com>
Signed-off-by: default avatarNicholas Bellinger <nab@linux-iscsi.org>
parent 4366b19c

drivers/infiniband/ulp/isert/ib_isert.c

+18 −8
Original line number Diff line number Diff line
@@ -1315,9 +1315,9 @@ isert_handle_scsi_cmd(struct isert_conn *isert_conn, 
{

	struct iscsi_conn *conn = isert_conn->conn;

	struct iscsi_scsi_req *hdr = (struct iscsi_scsi_req *)buf;

	struct scatterlist *sg;

	int imm_data, imm_data_len, unsol_data, sg_nents, rc;

	bool dump_payload = false;

	unsigned int data_len;



	rc = iscsit_setup_scsi_cmd(conn, cmd, buf);

	if (rc < 0)
@@ -1326,7 +1326,10 @@ isert_handle_scsi_cmd(struct isert_conn *isert_conn, 
	imm_data = cmd->immediate_data;

	imm_data_len = cmd->first_burst_len;

	unsol_data = cmd->unsolicited_data;

	data_len = cmd->se_cmd.data_length;



	if (imm_data && imm_data_len == data_len)

		cmd->se_cmd.se_cmd_flags |= SCF_PASSTHROUGH_SG_TO_MEM_NOALLOC;

	rc = iscsit_process_scsi_cmd(conn, cmd, hdr);

	if (rc < 0) {

		return 0;
@@ -1338,13 +1341,20 @@ isert_handle_scsi_cmd(struct isert_conn *isert_conn, 
	if (!imm_data)

		return 0;



	sg = &cmd->se_cmd.t_data_sg[0];

	if (imm_data_len != data_len) {

		sg_nents = max(1UL, DIV_ROUND_UP(imm_data_len, PAGE_SIZE));



	isert_dbg("Copying Immediate SG: %p sg_nents: %u from %p imm_data_len: %d\n",

		  sg, sg_nents, &rx_desc->data[0], imm_data_len);



	sg_copy_from_buffer(sg, sg_nents, &rx_desc->data[0], imm_data_len);

		sg_copy_from_buffer(cmd->se_cmd.t_data_sg, sg_nents,

				    &rx_desc->data[0], imm_data_len);

		isert_dbg("Copy Immediate sg_nents: %u imm_data_len: %d\n",

			  sg_nents, imm_data_len);

	} else {

		sg_init_table(&isert_cmd->sg, 1);

		cmd->se_cmd.t_data_sg = &isert_cmd->sg;

		cmd->se_cmd.t_data_nents = 1;

		sg_set_buf(&isert_cmd->sg, &rx_desc->data[0], imm_data_len);

		isert_dbg("Transfer Immediate imm_data_len: %d\n",

			  imm_data_len);

	}



	cmd->write_data_done += imm_data_len;

drivers/infiniband/ulp/isert/ib_isert.h

+1 −0
Original line number Diff line number Diff line
@@ -139,6 +139,7 @@ struct isert_cmd { 
	struct iser_rx_desc	*rx_desc;

	struct isert_rdma_wr	rdma_wr;

	struct work_struct	comp_work;

	struct scatterlist	sg;

};



struct isert_device;