libbpf: Use implicit XSKMAP lookup from AF_XDP XDP program
authorBjörn Töpel <bjorn.topel@intel.com>
Tue, 22 Oct 2019 07:22:06 +0000 (09:22 +0200)
committerAlexei Starovoitov <ast@kernel.org>
Wed, 23 Oct 2019 17:03:52 +0000 (10:03 -0700)
commitd7d962a095474fcd94861d5f4cccada2e4215aae
tree476fba2fcb5dcea9bbaf8ea492e45ba5eae9f2ae
parent5e5b03d163e15a40b0fa57c70b4e8edd549b0b98
libbpf: Use implicit XSKMAP lookup from AF_XDP XDP program

In commit 43e74c0267a3 ("bpf_xdp_redirect_map: Perform map lookup in
eBPF helper") the bpf_redirect_map() helper learned to do map lookup,
which means that the explicit lookup in the XDP program for AF_XDP is
not needed for post-5.3 kernels.

This commit adds the implicit map lookup with default action, which
improves the performance for the "rx_drop" [1] scenario with ~4%.

For pre-5.3 kernels, the bpf_redirect_map() returns XDP_ABORTED, and a
fallback path for backward compatibility is entered, where explicit
lookup is still performed. This means a slight regression for older
kernels (an additional bpf_redirect_map() call), but I consider that a
fair punishment for users not upgrading their kernels. ;-)

v1->v2: Backward compatibility (Toke) [2]
v2->v3: Avoid masking/zero-extension by using JMP32 [3]

[1] # xdpsock -i eth0 -z -r
[2] https://lore.kernel.org/bpf/87pnirb3dc.fsf@toke.dk/
[3] https://lore.kernel.org/bpf/87v9sip0i8.fsf@toke.dk/

Suggested-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20191022072206.6318-1-bjorn.topel@gmail.com
tools/lib/bpf/xsk.c