Commit e6a622fd authored by Sagi Grimberg's avatar Sagi Grimberg Committed by Jens Axboe
Browse files

nvmet: support fabrics sq flow control 



Technical proposal 8005 "fabrics SQ flow control" introduces a mode
where a host and controller agree to omit sq_head pointer updates
when sending nvme completions.

In case the host indicated desire to operate in this mode (connect attribute)
the controller will return back a connect completion with sq_head value
of 0xffff as indication that it will omit sq_head pointer updates.

This mode saves us an atomic update in the I/O path.

Reviewed-by: default avatarHannes Reinecke <hare@suse.com>
[hch: suggested better implementation]
Signed-off-by: default avatarSagi Grimberg <sagi@grimberg.me>
Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 6e2e312e

drivers/nvme/target/core.c

+13 −10
Original line number Diff line number Diff line
@@ -597,26 +597,28 @@ struct nvmet_ns *nvmet_ns_alloc(struct nvmet_subsys *subsys, u32 nsid) 
	return ns;

}



static void __nvmet_req_complete(struct nvmet_req *req, u16 status)

static void nvmet_update_sq_head(struct nvmet_req *req)

{

	if (req->sq->size) {

		u32 old_sqhd, new_sqhd;

	u16 sqhd;



	if (status)

		nvmet_set_status(req, status);



	if (req->sq->size) {

		do {

			old_sqhd = req->sq->sqhd;

			new_sqhd = (old_sqhd + 1) % req->sq->size;

		} while (cmpxchg(&req->sq->sqhd, old_sqhd, new_sqhd) !=

					old_sqhd);

	}

	sqhd = req->sq->sqhd & 0x0000FFFF;

	req->rsp->sq_head = cpu_to_le16(sqhd);

	req->rsp->sq_head = cpu_to_le16(req->sq->sqhd & 0x0000FFFF);

}



static void __nvmet_req_complete(struct nvmet_req *req, u16 status)

{

	if (!req->sq->sqhd_disabled)

		nvmet_update_sq_head(req);

	req->rsp->sq_id = cpu_to_le16(req->sq->qid);

	req->rsp->command_id = req->cmd->common.command_id;



	if (status)

		nvmet_set_status(req, status);

	if (req->ns)

		nvmet_put_namespace(req->ns);

	req->ops->queue_response(req);
@@ -765,6 +767,7 @@ bool nvmet_req_init(struct nvmet_req *req, struct nvmet_cq *cq, 
	req->sg_cnt = 0;

	req->transfer_len = 0;

	req->rsp->status = 0;

	req->rsp->sq_head = 0;

	req->ns = NULL;



	/* no support for fused commands yet */

drivers/nvme/target/fabrics-cmd.c

+6 −0
Original line number Diff line number Diff line
@@ -115,6 +115,12 @@ static u16 nvmet_install_queue(struct nvmet_ctrl *ctrl, struct nvmet_req *req) 
	/* note: convert queue size from 0's-based value to 1's-based value */

	nvmet_cq_setup(ctrl, req->cq, qid, sqsize + 1);

	nvmet_sq_setup(ctrl, req->sq, qid, sqsize + 1);



	if (c->cattr & NVME_CONNECT_DISABLE_SQFLOW) {

		req->sq->sqhd_disabled = true;

		req->rsp->sq_head = cpu_to_le16(0xffff);

	}



	return 0;

}

drivers/nvme/target/nvmet.h

+1 −0
Original line number Diff line number Diff line
@@ -106,6 +106,7 @@ struct nvmet_sq { 
	u16			qid;

	u16			size;

	u32			sqhd;

	bool			sqhd_disabled;

	struct completion	free_done;

	struct completion	confirm_done;

};

include/linux/nvme.h

+4 −0
Original line number Diff line number Diff line
@@ -1044,6 +1044,10 @@ struct nvmf_disc_rsp_page_hdr { 
	struct nvmf_disc_rsp_page_entry entries[0];

};



enum {

	NVME_CONNECT_DISABLE_SQFLOW	= (1 << 2),

};



struct nvmf_connect_command {

	__u8		opcode;

	__u8		resv1;

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