Every devmem dmabuf binding hands the page_pool PAGE_SIZE niovs today.
On NICs that consume one descriptor per netmem, this caps a single RX
descriptor at PAGE_SIZE and burns CPU on buffer churn.
In this series, we add a bind-time netlink attribute,
NETDEV_A_DMABUF_RX_BUF_SIZE, that lets userspace request a larger niov
size (power of two >= PAGE_SIZE). Drivers must opt in via
queue_mgmt_ops.QCFG_RX_PAGE_SIZE.
Measurements:
Setup: kperf devmem RX/TX cuda, 4 flows, 64 MB messages, 60s, dctcp,
num-rx-queues=4, dmabuf-rx/tx-size-mb=2048, 10 runs per niov size,
mlx5.
niov RX dev Gbps RX flow avg Gbps app sys %
----- ---------------- ----------------- ----------------
4K 300.63 +/- 53.21 75.16 +/- 13.30 54.15 +/- 10.23
16K 321.35 +/- 28.20 80.34 +/- 7.05 41.05 +/- 8.87
32K 347.63 +/- 2.20 86.91 +/- 0.55 44.54 +/- 3.51
64K 332.11 +/- 14.26 83.03 +/- 3.56 35.47 +/- 3.11
RX app sys % drops ~19% from 4K to 64K.
kperf support (not yet merged):
https://github.com/facebookexperimental/kperf/commit/8837577f920876bce6986ec18869ac04439ebcd2
Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
---
Changes in v6:
- Rename rx-buf-size to rx-page-size (Jakub)
- Move the >= PAGE_SIZE check into the netlink policy; doit only checks
is_power_of_2() (Jakub)
- Drop @ksft_disruptive from check_rx_large_niov() (Jakub)
- Link to v5: https://lore.kernel.org/r/20260708-tcpdm-large-niovs-v5-0-34bf6fac941b@meta.com
Changes in v5:
- removed unnecessary change from ssize_t to size_t (Mina)
- removed '--------' lines in the commit message (Paolo)
- removed commit msg about CONFIG_HUGETLB since that change was already
merged
- Link to v4: https://lore.kernel.org/r/20260701-tcpdm-large-niovs-v4-0-ca4654f37570@meta.com
Changes in v4:
- ncdevmem: fix the possible overflow in ncdevmem (Sashiko)
- drop the udmabuf patch because the fix is now already in net-next
- silenced two pylint complaints in devmem_lib.py
- Link to v3: https://lore.kernel.org/r/20260612-tcpdm-large-niovs-v3-0-a3b693e76fcb@meta.com
Changes in v3:
- fix a bunch of non-reverse christmas tree declarations (Stan)
- remove extra uint32 cast for getpagesize() (Stan)
- remove overzealous strtoul checking (Stan)
- remove value checks that the kernel already performs on rx_buf_size
(Stan)
- Link to v2: https://lore.kernel.org/r/20260611-tcpdm-large-niovs-v2-0-ee2bf15e7523@meta.com
Changes in v2:
- Use NL_SET_ERR_MSG_FMT for sg alignment failure details (Stan)
- Keep -E2BIG (not a direct ask, but seemed preferred, Stan)
- Update udmabuf commit message and comments explaining why
"one sg ent per folio" is useful (Christian)
- Set/restore nr_hugepages in py harness (Stan)
- Link to v1: https://lore.kernel.org/r/20260603-tcpdm-large-niovs-v1-0-f37a4ac6726c@meta.com
---
Bobby Eshleman (3):
net: devmem: allow rx-page-size > PAGE_SIZE per dmabuf binding
selftests/net: ncdevmem: add -b option to set rx-page-size on bind
selftests/net: devmem.py: add check_rx_large_niov
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 +
tools/testing/selftests/drivers/net/hw/devmem.py | 11 +++-
.../testing/selftests/drivers/net/hw/devmem_lib.py | 59 +++++++++++++++++++++-
tools/testing/selftests/drivers/net/hw/ncdevmem.c | 36 +++++++++++--
.../testing/selftests/drivers/net/hw/nk_devmem.py | 10 +++-
12 files changed, 190 insertions(+), 37 deletions(-)
---
base-commit: 89d8006259b81dd25c962f6cc8d7ab268d6ea426
change-id: 20260602-tcpdm-large-niovs-56523a3a1077
Best regards,
--
Bobby Eshleman <bobbyeshleman@meta.com>