[PATCH v4 0/2] nvme-tcp: allow setting per-queue io_cpu through sysfs

[Saravanan D <saravanand@crusoe.ai>]

On hosts that partition their CPUs after connect time, the connect
time io_cpu selection can land a queue's socket work on CPUs owned by
a different workload. This series lets a control plane set each
queue's io_cpu directly through sysfs.

The first patch adds a small common queue info that a transport embeds
in its queue structure, backing a transport neutral

  /sys/class/nvme/nvmeX/queues/<qid>/

directory under the controller device. The second patch has nvme-tcp
expose io_cpu and managed attributes there.

Changes since v3 [1]:
- Split into two patches and introduced the common queue info that
  Sagi proposed [2], named nvme_queue_info since the PCI driver
  already uses nvme_queue, as Nilay pointed out.
- Renamed the tcp_queues directory to queues so the ABI does not bake
  in the transport, as suggested by Nilay [3].
- Added the read-only managed attribute, 1 while io_cpu is driver
  managed and 0 once the user assigned it, as suggested by Nilay.
- io_cpu now accepts -1 or the string "unbound" to leave the socket
  work unbound, instead of restoring the connect time selection, as
  suggested by Sagi.
- A user assignment is tracked in the common queue info flags and
  still persists across reconnects, following Sagi's earlier guidance
  that io_cpu should not change on reconnect.
- The queue directories register once per controller lifetime and
  persist across reconnects, and the io_cpu accounting moved from the
  queue lock to a controller level lock since a write can now arrive
  while a queue is torn down.
- The io_cpu accounting now also covers a pin to a queue whose connect
  time pick did not bind a cpu, and the queue teardown clears any
  accounting left by a write racing the teardown.

[1] https://lore.kernel.org/linux-nvme/20260909211432.6741-1-saravanand@crusoe.ai/
[2] https://lore.kernel.org/linux-nvme/13c160d0-0657-47ce-9a16-58d348267ab0@grimberg.me/
[3] https://lore.kernel.org/linux-nvme/8dfee10f-89f3-463b-8d16-587873c3394c@linux.ibm.com/

Saravanan D (2):
  nvme: add per-queue sysfs directories
  nvme-tcp: allow setting per-queue io_cpu through sysfs

 Documentation/ABI/stable/sysfs-nvme |  21 ++++
 drivers/nvme/host/core.c            |   2 +
 drivers/nvme/host/nvme.h            |  23 +++++
 drivers/nvme/host/sysfs.c           |  42 ++++++++
 drivers/nvme/host/tcp.c             | 153 +++++++++++++++++++++++++++-
 5 files changed, 240 insertions(+), 1 deletion(-)


base-commit: 2ee54f01f07c0307deaf90ca8691a4643ae0357b
-- 
2.55.0