This series improves the CPU cost of RX token management by adding an attribute to NETDEV_CMD_BIND_RX that configures sockets using the binding to avoid the xarray allocator and instead use a per-binding niov array and a uref field in niov.
Improvement is ~13% cpu util per RX user thread.
Using kperf, the following results were observed:
Before: Average RX worker idle %: 13.13, flows 4, test runs 11 After: Average RX worker idle %: 26.32, flows 4, test runs 11
Two other approaches were tested, but with no improvement. Namely, 1) using a hashmap for tokens and 2) keeping an xarray of atomic counters but using RCU so that the hotpath could be mostly lockless. Neither of these approaches proved better than the simple array in terms of CPU.
The attribute NETDEV_A_DMABUF_AUTORELEASE is added to toggle the optimization. It is an optional attribute and defaults to 0 (i.e., optimization on).
Signed-off-by: Bobby Eshleman bobbyeshleman@meta.com
Changes in v9: - fixed build with NET_DEVMEM=n - fixed bug in rx bindings count logic - Link to v8: https://lore.kernel.org/r/20260107-scratch-bobbyeshleman-devmem-tcp-token-up...
Changes in v8: - change static branch logic (only set when enabled, otherwise just always revert back to disabled) - fix missing tests - Link to v7: https://lore.kernel.org/r/20251119-scratch-bobbyeshleman-devmem-tcp-token-up...
Changes in v7: - use netlink instead of sockopt (Stan) - restrict system to only one mode, dmabuf bindings can not co-exist with different modes (Stan) - use static branching to enforce single system-wide mode (Stan) - Link to v6: https://lore.kernel.org/r/20251104-scratch-bobbyeshleman-devmem-tcp-token-up...
Changes in v6: - renamed 'net: devmem: use niov array for token management' to refer to optionality of new config - added documentation and tests - make autorelease flag per-socket sockopt instead of binding field / sysctl - many per-patch changes (see Changes sections per-patch) - Link to v5: https://lore.kernel.org/r/20251023-scratch-bobbyeshleman-devmem-tcp-token-up...
Changes in v5: - add sysctl to opt-out of performance benefit, back to old token release - Link to v4: https://lore.kernel.org/all/20250926-scratch-bobbyeshleman-devmem-tcp-token-...
Changes in v4: - rebase to net-next - Link to v3: https://lore.kernel.org/r/20250926-scratch-bobbyeshleman-devmem-tcp-token-up...
Changes in v3: - make urefs per-binding instead of per-socket, reducing memory footprint - fallback to cleaning up references in dmabuf unbind if socket leaked tokens - drop ethtool patch - Link to v2: https://lore.kernel.org/r/20250911-scratch-bobbyeshleman-devmem-tcp-token-up...
Changes in v2: - net: ethtool: prevent user from breaking devmem single-binding rule (Mina) - pre-assign niovs in binding->vec for RX case (Mina) - remove WARNs on invalid user input (Mina) - remove extraneous binding ref get (Mina) - remove WARN for changed binding (Mina) - always use GFP_ZERO for binding->vec (Mina) - fix length of alloc for urefs - use atomic_set(, 0) to initialize sk_user_frags.urefs - Link to v1: https://lore.kernel.org/r/20250902-scratch-bobbyeshleman-devmem-tcp-token-up...
--- Bobby Eshleman (5): net: devmem: rename tx_vec to vec in dmabuf binding net: devmem: refactor sock_devmem_dontneed for autorelease split net: devmem: implement autorelease token management net: devmem: document NETDEV_A_DMABUF_AUTORELEASE netlink attribute selftests: drv-net: devmem: add autorelease test
Documentation/netlink/specs/netdev.yaml | 12 +++ Documentation/networking/devmem.rst | 70 +++++++++++++ include/net/netmem.h | 1 + include/net/sock.h | 7 +- include/uapi/linux/netdev.h | 1 + net/core/devmem.c | 116 ++++++++++++++++++---- net/core/devmem.h | 29 +++++- net/core/netdev-genl-gen.c | 5 +- net/core/netdev-genl.c | 10 +- net/core/sock.c | 103 ++++++++++++++----- net/ipv4/tcp.c | 76 +++++++++++--- net/ipv4/tcp_ipv4.c | 11 +- net/ipv4/tcp_minisocks.c | 3 +- tools/include/uapi/linux/netdev.h | 1 + tools/testing/selftests/drivers/net/hw/devmem.py | 21 +++- tools/testing/selftests/drivers/net/hw/ncdevmem.c | 19 ++-- 16 files changed, 407 insertions(+), 78 deletions(-) --- base-commit: 6ad078fa0ababa8de2a2b39f476d2abd179a3cf6 change-id: 20250829-scratch-bobbyeshleman-devmem-tcp-token-upstream-292be174d503
Best regards,