Commit d1de61db authored by Pavel Begunkov's avatar Pavel Begunkov
Browse files

io_uring/zcrx: document area chunking parameter 



struct io_uring_zcrx_ifq_reg::rx_buf_len is used as a hint specifying
the kernel what buffer size it should use. Document the API and
limitations.

Signed-off-by: default avatarPavel Begunkov <asml.silence@gmail.com>
parent a32bb32d

Documentation/networking/iou-zcrx.rst

+20 −0
Original line number Diff line number Diff line
@@ -196,6 +196,26 @@ Return buffers back to the kernel to be used again:: 
  rqe->len = cqe->res;

  IO_URING_WRITE_ONCE(*refill_ring.ktail, ++refill_ring.rq_tail);



Area chunking

-------------



zcrx splits the memory area into fixed-length physically contiguous chunks.

This limits the maximum buffer size returned in a single io_uring CQE. Users

can provide a hint to the kernel to use larger chunks by setting the

``rx_buf_len`` field of ``struct io_uring_zcrx_ifq_reg`` to the desired length

during registration. If this field is set to zero, the kernel defaults to

the system page size.



To use larger sizes, the memory area must be backed by physically contiguous

ranges whose sizes are multiples of ``rx_buf_len``. It also requires kernel

and hardware support. If registration fails, users are generally expected to

fall back to defaults by setting ``rx_buf_len`` to zero.



Larger chunks don't give any additional guarantees about buffer sizes returned

in CQEs, and they can vary depending on many factors like traffic pattern,

hardware offload, etc. It doesn't require any application changes beyond zcrx

registration.



Testing

=======