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nvmet: support fabrics sq flow control

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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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6
drivers/nvme/target/fabrics-cmd.c
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@@ -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;
}