[PATCH v5 0/2] nvme-tcp: allow setting per-queue io_cpu through sysfs

[Saravanan D]

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 core helpers for a transport neutral

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

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

Changes since v4 [1]:
- Rebased onto nvme-7.4, which sets up the I/O queues in parallel
  (61b0ed3be81b) and serializes the io_cpu accounting with
  nvme_tcp_cpu_queues_lock. The per controller io_cpu_lock is gone,
  and the io_cpu writes take nvme_tcp_cpu_queues_lock instead.
- A queue's directory now follows the queue's allocation, added in
  nvme_tcp_alloc_queue() and removed in nvme_tcp_free_queue(), so the
  directories match the queue count after a reconnect (Nilay). The
  core allocates each directory and its release frees only that
  allocation, which drops the transport's reference counting and
  completion (Nilay) and fixes the use after free, the controller
  leak and the teardown hang found by the Sashiko review of v4 [2].
- The transport creates the queues directory once before the parallel
  queue setup, and the kerneldoc states which calls may run
  concurrently (Nilay).
- The user assignment flag moved from the core into the nvme-tcp
  queue flags (Nilay).
- io_cpu is read through nvme_tcp_queue_io_cpu() and written through
  nvme_tcp_queue_change_io_cpu(), which carries __must_hold() for the
  context analysis (Nilay).
- The sysfs store collapsed to a single path and no longer checks
  NVME_TCP_Q_ALLOCATED, since the directory only exists while the
  queue is allocated (Nilay).
- The queue stop now clears NVME_TCP_Q_IO_CPU_SET under
  nvme_tcp_cpu_queues_lock, since a store may move io_cpu between the
  clear and the decrement.
- nvme_tcp_free_queue() drops NVME_TCP_Q_IO_CPU_SET, which also fixes
  a ledger count leaked by every failed I/O queue connect.
- io_cpu parses a decimal cpu number, and the ABI entry describes the
  directory lifetime, persistence across CPU offline and the behavior
  with wq_unbound.

[1] https://lore.kernel.org/linux-nvme/20260927070925.47209-1-saravanand@crusoe.ai/
[2] https://sashiko.dev/#/patchset/20260927070925.47209-1-saravanand%40crusoe.ai

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

 Documentation/ABI/stable/sysfs-nvme |  29 +++++
 drivers/nvme/host/core.c            |   6 +
 drivers/nvme/host/nvme.h            |  23 ++++
 drivers/nvme/host/sysfs.c           |  88 ++++++++++++++
 drivers/nvme/host/tcp.c             | 173 ++++++++++++++++++++++++----
 5 files changed, 299 insertions(+), 20 deletions(-)


base-commit: 2e8e30b3cf9f165e1a1d079331543cb7f2ad0e0c
-- 
2.55.0