* [PATCH bpf-next] libbpf: remove explicit XSKMAP lookup from AF_XDP XDP program
@ 2019-10-20 17:07 Björn Töpel
2019-10-20 19:53 ` Toke Høiland-Jørgensen
0 siblings, 1 reply; 3+ messages in thread
From: Björn Töpel @ 2019-10-20 17:07 UTC (permalink / raw)
To: netdev, ast, daniel
Cc: Björn Töpel, bpf, magnus.karlsson, magnus.karlsson,
toke, sridhar.samudrala
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%.
[1] # xdpsock -i eth0 -z -r
Suggested-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
---
tools/lib/bpf/xsk.c | 24 +++++-------------------
1 file changed, 5 insertions(+), 19 deletions(-)
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(),
--
2.20.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH bpf-next] libbpf: remove explicit XSKMAP lookup from AF_XDP XDP program
2019-10-20 17:07 [PATCH bpf-next] libbpf: remove explicit XSKMAP lookup from AF_XDP XDP program Björn Töpel
@ 2019-10-20 19:53 ` Toke Høiland-Jørgensen
2019-10-21 5:03 ` Björn Töpel
0 siblings, 1 reply; 3+ messages in thread
From: Toke Høiland-Jørgensen @ 2019-10-20 19:53 UTC (permalink / raw)
To: Björn Töpel, netdev, ast, daniel
Cc: Björn Töpel, bpf, magnus.karlsson, magnus.karlsson,
sridhar.samudrala
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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH bpf-next] libbpf: remove explicit XSKMAP lookup from AF_XDP XDP program
2019-10-20 19:53 ` Toke Høiland-Jørgensen
@ 2019-10-21 5:03 ` Björn Töpel
0 siblings, 0 replies; 3+ messages in thread
From: Björn Töpel @ 2019-10-21 5:03 UTC (permalink / raw)
To: Toke Høiland-Jørgensen
Cc: Netdev, Alexei Starovoitov, Daniel Borkmann,
Björn Töpel, bpf, Magnus Karlsson, Karlsson, Magnus,
Samudrala, Sridhar
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
>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2019-10-20 17:07 [PATCH bpf-next] libbpf: remove explicit XSKMAP lookup from AF_XDP XDP program Björn Töpel
2019-10-20 19:53 ` Toke Høiland-Jørgensen
2019-10-21 5:03 ` Björn Töpel
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