This series expands the XDP TX metadata framework to allow user applications to pass per packet 64-bit launch time directly to the kernel driver, requesting launch time hardware offload support. The XDP TX metadata framework will not perform any clock conversion or packet reordering.
Please note that the role of Tx metadata is just to pass the launch time, not to enable the offload feature. Users will need to enable the launch time hardware offload feature of the device by using the respective command, such as the tc-etf command.
Although some devices use the tc-etf command to enable their launch time hardware offload feature, xsk packets will not go through the etf qdisc. Therefore, in my opinion, the launch time should always be based on the PTP Hardware Clock (PHC). Thus, i did not include a clock ID to indicate the clock source.
To simplify the test steps, I modified the xdp_hw_metadata bpf self-test tool in such a way that it will set the launch time based on the offset provided by the user and the value of the Receive Hardware Timestamp, which is against the PHC. This will eliminate the need to discipline System Clock with the PHC and then use clock_gettime() to get the time.
Please note that AF_XDP lacks a feedback mechanism to inform the application if the requested launch time is invalid. So, users are expected to familiar with the horizon of the launch time of the device they use and not request a launch time that is beyond the horizon. Otherwise, the driver might interpret the launch time incorrectly and react wrongly. For stmmac and igc, where modulo computation is used, a launch time larger than the horizon will cause the device to transmit the packet earlier that the requested launch time.
Although there is no feedback mechanism for the launch time request for now, user still can check whether the requested launch time is working or not, by requesting the Transmit Completion Hardware Timestamp.
V7: - split the refactoring code of igc empty packet insertion into a separate commit (Faizal) - add explanation on why the value "4" is used as igc transmit budget (Faizal) - perform a stress test by sending 1000 packets with 10ms interval and launch time set to 500us in the future (Faizal & Yong Liang)
V6: https://lore.kernel.org/netdev/20250116155350.555374-1-yoong.siang.song@inte... - fix selftest build errors by using asprintf() and realloc(), instead of managing the buffer sizes manually (Daniel, Stanislav)
V5: https://lore.kernel.org/netdev/20250114152718.120588-1-yoong.siang.song@inte... - change netdev feature name from tx-launch-time to tx-launch-time-fifo to explicitly state the FIFO behaviour (Stanislav) - improve the looping of xdp_hw_metadata app to wait for packet tx completion to be more readable by using clock_gettime() (Stanislav) - add launch time setup steps into xdp_hw_metadata app (Stanislav)
V4: https://lore.kernel.org/netdev/20250106135506.9687-1-yoong.siang.song@intel.... - added XDP launch time support to the igc driver (Jesper & Florian) - added per-driver launch time limitation on xsk-tx-metadata.rst (Jesper) - added explanation on FIFO behavior on xsk-tx-metadata.rst (Jakub) - added step to enable launch time in the commit message (Jesper & Willem) - explicitly documented the type of launch_time and which clock source it is against (Willem)
V3: https://lore.kernel.org/netdev/20231203165129.1740512-1-yoong.siang.song@int... - renamed to use launch time (Jesper & Willem) - changed the default launch time in xdp_hw_metadata apps from 1s to 0.1s because some NICs do not support such a large future time.
V2: https://lore.kernel.org/netdev/20231201062421.1074768-1-yoong.siang.song@int... - renamed to use Earliest TxTime First (Willem) - renamed to use txtime (Willem)
V1: https://lore.kernel.org/netdev/20231130162028.852006-1-yoong.siang.song@inte...
Song Yoong Siang (5): xsk: Add launch time hardware offload support to XDP Tx metadata selftests/bpf: Add launch time request to xdp_hw_metadata net: stmmac: Add launch time support to XDP ZC igc: Refactor empty packet insertion into a reusable function igc: Add launch time support to XDP ZC
Documentation/netlink/specs/netdev.yaml | 4 + Documentation/networking/xsk-tx-metadata.rst | 62 +++++++ drivers/net/ethernet/intel/igc/igc_main.c | 84 ++++++--- drivers/net/ethernet/stmicro/stmmac/stmmac.h | 2 + .../net/ethernet/stmicro/stmmac/stmmac_main.c | 13 ++ include/net/xdp_sock.h | 10 ++ include/net/xdp_sock_drv.h | 1 + include/uapi/linux/if_xdp.h | 10 ++ include/uapi/linux/netdev.h | 3 + net/core/netdev-genl.c | 2 + net/xdp/xsk.c | 3 + tools/include/uapi/linux/if_xdp.h | 10 ++ tools/include/uapi/linux/netdev.h | 3 + tools/testing/selftests/bpf/xdp_hw_metadata.c | 168 +++++++++++++++++- 14 files changed, 348 insertions(+), 27 deletions(-)