Message ID | 20191020170711.22082-1-bjorn.topel@gmail.com |
---|---|
State | Changes Requested |
Delegated to: | BPF Maintainers |
Headers | show |
Series | [bpf-next] libbpf: remove explicit XSKMAP lookup from AF_XDP XDP program | expand |
Björn Töpel <bjorn.topel@gmail.com> writes: > From: Björn Töpel <bjorn.topel@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. > > This commit removes the map lookup, which simplifies the BPF code and > improves the performance for the "rx_drop" [1] scenario with ~4%. Nice, 4% is pretty good! I wonder if the program needs to be backwards-compatible (with pre-5.3 kernels), though? You can do that by something like this: ret = bpf_redirect_map(&xsks_map, index, XDP_PASS); if (ret > 0) return ret; if (bpf_map_lookup_elem(&xsks_map, &index)) return bpf_redirect_map(&xsks_map, index, 0); return XDP_PASS; This works because bpf_redirect_map() prior to 43e74c0267a3 will return XDP_ABORTED on a non-0 flags value. -Toke
On Sun, 20 Oct 2019 at 21:53, Toke Høiland-Jørgensen <toke@redhat.com> wrote: > > Björn Töpel <bjorn.topel@gmail.com> writes: > > > From: Björn Töpel <bjorn.topel@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. > > > > This commit removes the map lookup, which simplifies the BPF code and > > improves the performance for the "rx_drop" [1] scenario with ~4%. > > Nice, 4% is pretty good! > > I wonder if the program needs to be backwards-compatible (with pre-5.3 > kernels), though? > > You can do that by something like this: > > ret = bpf_redirect_map(&xsks_map, index, XDP_PASS); > if (ret > 0) > return ret; > > if (bpf_map_lookup_elem(&xsks_map, &index)) > return bpf_redirect_map(&xsks_map, index, 0); > return XDP_PASS; > Ah, yes. Thanks for pointing that out. I'll do a respin. Thanks, Björn > > This works because bpf_redirect_map() prior to 43e74c0267a3 will return > XDP_ABORTED on a non-0 flags value. > > -Toke >
diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c index b0f532544c91..8e35de3cb443 100644 --- a/tools/lib/bpf/xsk.c +++ b/tools/lib/bpf/xsk.c @@ -278,29 +278,15 @@ static int xsk_load_xdp_prog(struct xsk_socket *xsk) * * // A set entry here means that the correspnding queue_id * // has an active AF_XDP socket bound to it. - * if (bpf_map_lookup_elem(&xsks_map, &index)) - * return bpf_redirect_map(&xsks_map, index, 0); - * - * return XDP_PASS; + * return bpf_redirect_map(&xsks_map, index, 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), - BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), - BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), - BPF_LD_MAP_FD(BPF_REG_1, xsk->xsks_map_fd), - BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem), - BPF_MOV64_REG(BPF_REG_1, BPF_REG_0), - BPF_MOV32_IMM(BPF_REG_0, 2), - /* if r1 == 0 goto +5 */ - BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0, 5), - /* r2 = *(u32 *)(r10 - 4) */ + /* r2 = *(u32 *)(r1 + 16) */ + BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, 16), 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), + /* r3 = XDP_PASS */ + BPF_MOV32_IMM(BPF_REG_3, 2), BPF_EMIT_CALL(BPF_FUNC_redirect_map), /* The jumps are to this instruction */ BPF_EXIT_INSN(),