[PATCH 0/5] pci: nvmet: support completion queue sharing by multiple submission queues

[Wilfred Mallawa]

From: Wilfred Mallawa <wilfred.mallawa at wdc.com>

Hi all,

For the NVMe PCI transport, the NVMe specification allows different
submission queues (SQs) to share completion queues (CQs), however,
this is not supported in the current NVMe target implementation.
Until now, the nvmet target implementation enforced a 1:1 relationship
between SQs and CQs, which is not specification compliant for the NVMe
PCI transport.

This patch series adds support for CQ sharing between multiple SQs in the
NVMe target driver, in line with the NVMe PCI transport specification.
This series implements reference counting for completion queues to ensure
proper lifecycle management when shared across multiple submission queues.
This ensures that we retain CQs until all referencing SQs are deleted
first, thereby avoiding premature CQ deletions.

Sample callchain with CQ refcounting for the PCI endpoint target
(pci-epf)
=================================================================

i.   nvmet_execute_create_cq -> nvmet_pci_epf_create_cq -> nvmet_cq_create
     -> nvmet_cq_init			[cq refcount = 1]

ii.  nvmet_execute_create_sq -> nvmet_pci_epf_create_sq -> nvmet_sq_create
     -> nvmet_sq_init -> nvmet_cq_get	[cq refcount = 2]

iii. nvmet_execute_delete_sq -> nvmet_pci_epf_delete_sq ->
     nvmet_sq_destroy -> nvmet_cq_put	[cq refcount = 1]

iv.  nvmet_execute_delete_cq -> nvmet_pci_epf_delete_cq -> nvmet_cq_put
					[cq refcount = 0]

For NVMe over fabrics, CQ sharing is not supported per specification,
however, the fabrics drivers are updated to integrate the new
API changes. No functional change is intended here.

Testing
=======

Core functionality changes were tested with a Rockchip-based Rock5B PCIe
endpoint setup using the pci-epf driver. The host kernel was modified to
support queue sharing. In the test setup, this resulted in IO SQs 1 & 2
using IO CQ 1 and IO SQ 3 & 4 using IO CQ 2.

Testing methodology includes:

For PCI:

1. Boot up host
2. Assert that the endpoint device is detected as an NVMe drive
   (IO CQs/SQs are created)
3. Run FIOs
4. Unbind NVMe driver (IO SQs then CQs are deleted)
5. Rebind NVMe driver (IO SQs then CQs are created)
6. Run FIOs

For NVMe over fabrics: Using NVMe loop driver:

Note that there is no queue sharing supported for fabrics.

1. Connect command (IO queues are created)
2. Run FIOs
3. Disconnect command (IO queues are deleted)

Thanks!

Wilfred Mallawa (5):
  nvmet: add a helper function for cqid checking
  nvmet: cq: prepare for completion queue sharing
  nvmet: fabrics: add CQ init and destroy
  nvmet: support completion queue sharing
  nvmet: Simplify nvmet_req_init() interface

 drivers/nvme/target/admin-cmd.c   | 31 ++++------
 drivers/nvme/target/core.c        | 94 ++++++++++++++++++++++++-------
 drivers/nvme/target/fabrics-cmd.c |  8 +++
 drivers/nvme/target/fc.c          | 10 ++--
 drivers/nvme/target/loop.c        | 23 +++++---
 drivers/nvme/target/nvmet.h       | 24 +++++---
 drivers/nvme/target/pci-epf.c     | 11 ++--
 drivers/nvme/target/rdma.c        |  8 ++-
 drivers/nvme/target/tcp.c         |  8 ++-
 9 files changed, 147 insertions(+), 70 deletions(-)

-- 
2.49.0