Merge tag 'net-queue-rx-buf-len-v9' of https://github.com/isilence/linux

Pavel Begunkov says:

====================
Add support for providers with large rx buffer

Many modern NICs support configurable receive buffer lengths, and zcrx and
memory providers can use buffers larger than 4K to improve performance.
When paired with hw-gro larger rx buffer sizes can drastically reduce
the number of buffers traversing the stack and save a lot of processing
time. It also allows to give to users larger contiguous chunks of data.

Single stream benchmarks showed up to ~30% CPU util improvement.
E.g. comparison for 4K vs 32K buffers using a 200Gbit NIC:

packets=23987040 (MB=2745098), rps=199559 (MB/s=22837)
CPU    %usr   %nice    %sys %iowait    %irq   %soft   %idle
  0    1.53    0.00   27.78    2.72    1.31   66.45    0.22
packets=24078368 (MB=2755550), rps=200319 (MB/s=22924)
CPU    %usr   %nice    %sys %iowait    %irq   %soft   %idle
  0    0.69    0.00    8.26   31.65    1.83   57.00    0.57

This series adds net infrastructure for memory providers configuring
the size and implements it for bnxt. It's an opt-in feature for drivers,
they should advertise support for the parameter in the qops and must check
if the hardware supports the given size. It's limited to memory providers
as it drastically simplifies implementation. It doesn't affect the fast
path zcrx uAPI, and the user exposed parameter is defined in zcrx terms,
which allows it to be flexible and adjusted in the future.

A liburing example can be found at [2]

full branch:
[1] https://github.com/isilence/linux.git zcrx/large-buffers-v8
Liburing example:
[2] https://github.com/isilence/liburing.git zcrx/rx-buf-len

* tag 'net-queue-rx-buf-len-v9' of https://github.com/isilence/linux:
  io_uring/zcrx: document area chunking parameter
  selftests: iou-zcrx: test large chunk sizes
  eth: bnxt: support qcfg provided rx page size
  eth: bnxt: adjust the fill level of agg queues with larger buffers
  eth: bnxt: store rx buffer size per queue
  net: pass queue rx page size from memory provider
  net: add bare bone queue configs
  net: reduce indent of struct netdev_queue_mgmt_ops members
  net: memzero mp params when closing a queue
====================

Link: https://patch.msgid.link/
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 20 insertions, 0 deletions

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
 =======