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: Pavel Begunkov asml.silence@gmail.com --- Documentation/networking/iou-zcrx.rst | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+)
diff --git a/Documentation/networking/iou-zcrx.rst b/Documentation/networking/iou-zcrx.rst index 54a72e172bdc..7f3f4b2e6cf2 100644 --- a/Documentation/networking/iou-zcrx.rst +++ b/Documentation/networking/iou-zcrx.rst @@ -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 =======