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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: Hannes Reinecke <hare@suse.com>
[hch: suggested better implementation]
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Sagi Grimberg 2018-11-19 14:11:12 -08:00 committed by Jens Axboe
parent 6e2e312ea7
commit e6a622fd6d
4 changed files with 24 additions and 10 deletions
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23
drivers/nvme/target/core.c
View File

@ -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)
{
u32 old_sqhd, new_sqhd;
u16 sqhd;
if (status)
nvmet_set_status(req, status);
if (req->sq->size) {
u32 old_sqhd, new_sqhd;
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 */

6
drivers/nvme/target/fabrics-cmd.c
View File

@ -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;
}

1
drivers/nvme/target/nvmet.h
View File

@ -106,6 +106,7 @@ struct nvmet_sq {
u16 qid;
u16 size;
u32 sqhd;
bool sqhd_disabled;
struct completion free_done;
struct completion confirm_done;
};

4
include/linux/nvme.h
View File

@ -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;