From: Björn Töpel <bjorn.to...@intel.com>
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]
[1] # xdpsock -i eth0 -z -r
[2] https://lore.kernel.org/bpf/87pnirb3dc....@toke.dk/
Suggested-by: Toke Høiland-Jørgensen <t...@redhat.com>
Signed-off-by: Björn Töpel <bjorn.to...@intel.com>
---
tools/lib/bpf/xsk.c | 45 +++++++++++++++++++++++++++++++++++----------
1 file changed, 35 insertions(+), 10 deletions(-)
diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index b0f532544c91..391a126b3fd8 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -274,33 +274,58 @@ static int xsk_load_xdp_prog(struct xsk_socket *xsk)
/* This is the C-program:
* SEC("xdp_sock") int xdp_sock_prog(struct xdp_md *ctx)
* {
- * int index = ctx->rx_queue_index;
+ * int ret, index = ctx->rx_queue_index;
*
* // A set entry here means that the correspnding queue_id
* // has an active AF_XDP socket bound to it.
+ * ret = bpf_redirect_map(&xsks_map, index, XDP_PASS);
+ * ret &= XDP_PASS | XDP_REDIRECT;
+ * if (ret)
+ * return ret;
+ *
+ * // Fallback for pre-5.3 kernels, not supporting default
+ * // action in the flags parameter.
* if (bpf_map_lookup_elem(&xsks_map, &index))
* return bpf_redirect_map(&xsks_map, index, 0);
- *
* return XDP_PASS;
* }
*/
struct bpf_insn prog[] = {
- /* r1 = *(u32 *)(r1 + 16) */
- BPF_LDX_MEM(BPF_W, BPF_REG_1, BPF_REG_1, 16),
- /* *(u32 *)(r10 - 4) = r1 */
- BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_1, -4),
+ /* r2 = *(u32 *)(r1 + 16) */
+ BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, 16),
+ /* *(u32 *)(r10 - 4) = r2 */
+ BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_2, -4),
+ /* r1 = xskmap[] */
+ BPF_LD_MAP_FD(BPF_REG_1, xsk->xsks_map_fd),
+ /* r3 = XDP_PASS */
+ BPF_MOV64_IMM(BPF_REG_3, 2),
+ /* call bpf_redirect_map */
+ BPF_EMIT_CALL(BPF_FUNC_redirect_map),
+ /* r0 &= XDP_PASS | XDP_REDIRECT */
+ BPF_ALU64_IMM(BPF_AND, BPF_REG_0, XDP_PASS | XDP_REDIRECT),
+ /* if r0 != 0 goto pc+13 */
+ BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 13),
+ /* r2 = r10 */
BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
+ /* r2 += -4 */
BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4),
+ /* r1 = xskmap[] */
BPF_LD_MAP_FD(BPF_REG_1, xsk->xsks_map_fd),
+ /* call bpf_map_lookup_elem */
BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
+ /* r1 = r0 */
BPF_MOV64_REG(BPF_REG_1, BPF_REG_0),
- BPF_MOV32_IMM(BPF_REG_0, 2),
- /* if r1 == 0 goto +5 */
+ /* r0 = XDP_PASS */
+ BPF_MOV64_IMM(BPF_REG_0, 2),
+ /* if r1 == 0 goto pc+5 */
BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0, 5),
/* r2 = *(u32 *)(r10 - 4) */
- BPF_LD_MAP_FD(BPF_REG_1, xsk->xsks_map_fd),
BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_10, -4),
- BPF_MOV32_IMM(BPF_REG_3, 0),
+ /* r1 = xskmap[] */
+ BPF_LD_MAP_FD(BPF_REG_1, xsk->xsks_map_fd),
+ /* r3 = 0 */
+ BPF_MOV64_IMM(BPF_REG_3, 0),
+ /* call bpf_redirect_map */
BPF_EMIT_CALL(BPF_FUNC_redirect_map),
/* The jumps are to this instruction */
BPF_EXIT_INSN(),
--
2.20.1
