Re: [PATCH net-next v6 1/3] net: devmem: allow rx-page-size > PAGE_SIZE per dmabuf binding

On Fri, Jul 24, 2026 at 02:21:15PM -0700, Bobby Eshleman wrote:

From: Bobby Eshleman <redacted>

Every devmem dmabuf binding today hands the page_pool PAGE_SIZE niovs.
This caps a single RX descriptor at PAGE_SIZE, burning CPU on buffer
churn for large flows.

Add a bind-time netlink attribute, NETDEV_A_DMABUF_RX_PAGE_SIZE, that
lets userspace request a larger niov size. The value must be a power of
two >= PAGE_SIZE.

Measurements:
Setup: kperf in devmem RX/TX cuda mode, 4 flows, 64 MB messages, 60s,
dctcp, num-rx-queues=4, dmabuf-rx/tx-size-mb=2048, 10 runs per niov
size, mlx5.

CPU Util:

   niov        net sirq %        net idle %         app sys %        app idle %
  -----  ----------------  ----------------  ----------------  ----------------
     4K   62.38 +/-  8.27   33.40 +/-  7.51   54.15 +/- 10.23   43.67 +/- 10.53
    16K   58.91 +/-  5.35   35.23 +/-  5.88   41.05 +/-  8.87   56.42 +/-  9.24
    32K   64.12 +/-  0.68   31.09 +/-  1.48   44.54 +/-  3.51   52.63 +/-  3.65
    64K   54.69 +/-  5.54   39.67 +/-  5.81   35.47 +/-  3.11   61.97 +/-  3.27

RX app sys % drops ~19% from 4K to 64K.

Throughput:

   niov       RX dev Gbps   RX flow avg Gbps
  -----  ----------------  -----------------
     4K  300.63 +/- 53.21    75.16 +/- 13.30
    16K  321.35 +/- 28.20    80.34 +/-  7.05
    32K  347.63 +/-  2.20    86.91 +/-  0.55
    64K  332.11 +/- 14.26    83.03 +/-  3.56

Throughput seems to increase, but the stdev is pretty wide so could just
be noise.

kperf support (not yet merged):
https://github.com/facebookexperimental/kperf/commit/8837577f920876bce6986ec18869ac04439ebcd2

Signed-off-by: Bobby Eshleman <redacted>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Reviewed-by: Mina Almasry <redacted>
---
 Documentation/netlink/specs/netdev.yaml | 17 ++++++++++++
 include/uapi/linux/netdev.h             |  1 +
 net/core/devmem.c                       | 49 +++++++++++++++++++--------------
 net/core/devmem.h                       | 13 ++++++---
 net/core/netdev-genl-gen.c              | 11 ++++++--
 net/core/netdev-genl-gen.h              |  1 +
 net/core/netdev-genl.c                  | 18 ++++++++++--
 tools/include/uapi/linux/netdev.h       |  1 +
 8 files changed, 83 insertions(+), 28 deletions(-)

LGTM,
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>

Cheers,
 Nik