On Fri, 16 Oct 2026 22:19:38 +0100 Frank Dressler <[email protected]> wrote:
> The third patch adds PACKET_IGNORE_OUTGOING which moves the > filtering into the kernel. It is supported since Linux 4.20 but only > works for single-queue AF_PACKET scenarios. Multi-queue AF_PACKET > is still filtered in the PMD. > > The fourth patch adds PACKET_FANOUT_FLAG_IGNORE_OUTGOING which is > supported since Linux 6.2 and moves the filtering into the kernel > for the multi-queue scenarios. The kernel does not expose a direct > way to check whether it supports PACKET_FANOUT_FLAG_IGNORE_OUTGOING > but it also does not return an error when the sockopt is set on > kernels that do not support it. Because of that the sockopt is set > opportunistically. The PMD check is kept, since older kernels accept > the flag without effect and support cannot be detected. > > Overall we get the following: > > | Single Queue | Multi-Queue > ------------+--------------+------------- > Kernel 5.4+ | in kernel | in PMD > Kernel 6.2+ | in kernel | in kernel > > I tested this on both, kernel 7.2.8 and kernel 5.4.0 with both single > and multiple queues. My results, strace'ing testpmd 7.2.8, with the > variants of ignore_outgoing=0|1 and single/multi-queue: > > Kernel 5.4.0: > qpairs=1,ignore_outgoing=0: - > qpairs=1,ignore_outgoing=1: setsockopt(14, SOL_PACKET, 0x17 /* > PACKET_??? */, [1], 4) = 0 > // 0x17 is PACKET_IGNORE_OUTGOING > > qpairs=2,ignore_outgoing=0: setsockopt(14, SOL_PACKET, PACKET_FANOUT, > [-1878917532], 4) = 0 > // -1878917532 does NOT contain PACKET_FANOUT_FLAG_IGNORE_OUTGOING<<16 > qpairs=2,ignore_outgoing=1: setsockopt(14, SOL_PACKET, PACKET_FANOUT, > [-805175699], 4) = 0 > // -805175699 does contain PACKET_FANOUT_FLAG_IGNORE_OUTGOING<<16 > > Kernel 7.2.8: > qpairs=1,ignore_outgoing=0: - > qpairs=1,ignore_outgoing=1: setsockopt(13, SOL_PACKET, > PACKET_IGNORE_OUTGOING, [1], 4) = 0 > > qpairs=2,ignore_outgoing=0: setsockopt(13, SOL_PACKET, PACKET_FANOUT, > [-1878978899], 4) = 0 > // -1878978899 does NOT contain PACKET_FANOUT_FLAG_IGNORE_OUTGOING<<16 > qpairs=2,ignore_outgoing=1: setsockopt(13, SOL_PACKET, PACKET_FANOUT, > [-805236964], 4) = 0 > // -805236964 does contain PACKET_FANOUT_FLAG_IGNORE_OUTGOING<<16 > > They show that the setsockopt succeeds even on the old kernel that > does not support PACKET_FANOUT_FLAG_IGNORE_OUTGOING, so setting it > opportunistically is fine. They also show that the code only tries to > set PACKET_FANOUT_FLAG_IGNORE_OUTGOING or PACKET_IGNORE_OUTGOING when > requested by ignore_outgoing=1. And it shows that > PACKET_IGNORE_OUTGOING is used for single and > PACKET_FANOUT_FLAG_IGNORE_OUTGOING for multi-queue. > > I have also manually ran testpmd in all modes and both kernels to > verify that ignore_outgoing works as expected, sending packets and > checking what testpmd was receiving (``set verbose 1``). > > > v7: > - log ignore_outgoing with %u > - use n_inject for both sides of the ignore_outgoing test > - mention Linux 4.20 once in the single-queue commit message > - keep the release note to the devarg, not where filtering happens Applied to next-net with simplification of the release note.
