Currently ublk zero-copy requires ublk request buffers to be registered and unregistered by the ublk I/O's daemon task. However, as currently implemented, there is no reason for this restriction. Registration looks up the request via the ublk device's tagset rather than the daemon-local ublk_io structure and takes an atomic reference to prevent racing with dispatch or completion of the request. Ming has expressed interest in relaxing this restriction[1] so the ublk server can offload the I/O operation that uses the zero-copy buffer to another thread. Additionally, optimize the buffer registration for the common case where the buffer is registered by the daemon task. Skip the expensive atomic reference count increment and the several pointer dereferences involved in looking up the request on the tagset. A few other cleanups and optimizations are included. [1]: https://lore.kernel.org/linux-block/aAmYJxaV1-yWEMRo@fedora/ Caleb Sander Mateos (8): ublk: check cmd_op first ublk: handle UBLK_IO_FETCH_REQ first ublk: remove task variable from __ublk_ch_uring_cmd() ublk: consolidate UBLK_IO_FLAG_{ACTIVE,OWNED_BY_SRV} checks ublk: move ublk_prep_cancel() to case UBLK_IO_COMMIT_AND_FETCH_REQ ublk: allow UBLK_IO_(UN)REGISTER_IO_BUF on any task ublk: optimize UBLK_IO_REGISTER_IO_BUF on daemon task ublk: remove ubq checks from ublk_{get,put}_req_ref() drivers/block/ublk_drv.c | 169 ++++++++++++++++++++-------------- include/uapi/linux/ublk_cmd.h | 8 ++ 2 files changed, 107 insertions(+), 70 deletions(-) -- 2.45.2
