diff options
| author | Caleb Sander Mateos <csander@purestorage.com> | 2026-08-03 15:14:37 -0600 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2026-08-03 20:32:10 -0600 |
| commit | 5c0958d80190822c4614ca00478d9acd9671bba6 (patch) | |
| tree | 3ad9465e39c3baeca1baeb3c31e1ba603721393f /include/uapi/linux | |
| parent | 735409f58b3da45094f2dfd7c18fb9e1937431f1 (diff) | |
ublk: add UBLK_F_IO_DESC_SIZE
ublk passes the parameters of incoming I/O in memory shared between the
kernel ublk driver and userspace ublk server in struct ublksrv_io_desc.
The size of this struct is currently fixed to 24 bytes, which has been
an obstacle to extending it with additional fields [1]. Additionally,
with multiple ublk server threads handling I/Os from the same ublk queue
(possible with UBLK_F_PER_IO_DAEMON or UBLK_F_BATCH_IO), false sharing
results from adjacent io_descs sharing the same cache line.
Add a ublk feature UBLK_F_IO_DESC_SIZE to allow a ublk server to
override the size of each io_desc. The size must be at least 24 and a
multiple of 8 to store a properly-aligned struct ublksrv_io_desc. It's
also limited to a maximum of 256, though this bound could be lifted in
the future.
The struct ublksrv_io_desc is located at the beginning of each io_desc
and the remainder is padding. The mmap() performed for each queue must
have a length of queue_depth * io_desc_size rounded up to the page size.
The mmap() offset must be q_id * UBLK_MAX_QUEUE_DEPTH * io_desc_size,
also rounded up to the page size.
[1]: https://lore.kernel.org/linux-block/aV8QfvaNO5P6vOs6@fedora/
Suggested-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Link: https://patch.msgid.link/20260803211441.2538144-6-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'include/uapi/linux')
| -rw-r--r-- | include/uapi/linux/ublk_cmd.h | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h index 6991370a72ce..33b25dd13965 100644 --- a/include/uapi/linux/ublk_cmd.h +++ b/include/uapi/linux/ublk_cmd.h @@ -417,6 +417,9 @@ struct ublk_shmem_buf_reg { */ #define UBLK_F_SHMEM_ZC (1ULL << 19) +/* ublksrv_io_desc size is specified by ublksrv_ctrl_dev_info's io_desc_size */ +#define UBLK_F_IO_DESC_SIZE (1ULL << 20) + /* device state */ #define UBLK_S_DEV_DEAD 0 #define UBLK_S_DEV_LIVE 1 @@ -452,7 +455,7 @@ struct ublksrv_ctrl_dev_info { __u16 nr_hw_queues; __u16 queue_depth; __u16 state; - __u16 pad0; + __u16 io_desc_size; __u32 max_io_buf_bytes; __u32 dev_id; |