[PATCH bpf-next] bpf: tcp: Improve bpf write tcp opt performance

[Feng zhou]

From: Feng Zhou <zhoufeng.zf@xxxxxxxxxxxxx>

Set the full package write tcp option, the test found that the loss
will be 20%. If a package wants to write tcp option, it will trigger
bpf prog three times, and call "tcp_send_mss" calculate mss_cache,
call "tcp_established_options" to reserve tcp opt len, call
"bpf_skops_write_hdr_opt" to write tcp opt, but "tcp_send_mss" before
TSO. Through bpftrace tracking, it was found that during the pressure
test, "tcp_send_mss" call frequency was 90w/s. Considering that opt
len does not change often, consider caching opt len for optimization.

Signed-off-by: Feng Zhou <zhoufeng.zf@xxxxxxxxxxxxx>
---
 include/linux/tcp.h            |  3 +++
 include/uapi/linux/bpf.h       |  8 +++++++-
 net/ipv4/tcp_output.c          | 12 +++++++++++-
 tools/include/uapi/linux/bpf.h |  8 +++++++-
 4 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 6a5e08b937b3..74437fcf94a2 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -455,6 +455,9 @@ struct tcp_sock {
 					  * to recur itself by calling
 					  * bpf_setsockopt(TCP_CONGESTION, "itself").
 					  */
+	u8	bpf_opt_len;		/* save tcp opt len implementation
+					 * BPF_SOCK_OPS_HDR_OPT_LEN_CB fast path
+					 */
 #define BPF_SOCK_OPS_TEST_FLAG(TP, ARG) (TP->bpf_sock_ops_cb_flags & ARG)
 #else
 #define BPF_SOCK_OPS_TEST_FLAG(TP, ARG) 0
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 90706a47f6ff..f2092de1f432 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -6892,8 +6892,14 @@ enum {
 	 * options first before the BPF program does.
 	 */
 	BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG = (1<<6),
+	/* Fast path to reserve space in a skb under
+	 * sock_ops->op == BPF_SOCK_OPS_HDR_OPT_LEN_CB.
+	 * opt length doesn't change often, so it can save in the tcp_sock. And
+	 * set BPF_SOCK_OPS_HDR_OPT_LEN_CACHE_CB_FLAG to no bpf call.
+	 */
+	BPF_SOCK_OPS_HDR_OPT_LEN_CACHE_CB_FLAG = (1<<7),
 /* Mask of all currently supported cb flags */
-	BPF_SOCK_OPS_ALL_CB_FLAGS       = 0x7F,
+	BPF_SOCK_OPS_ALL_CB_FLAGS       = 0xFF,
 };
 
 /* List of known BPF sock_ops operators.
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index ea7ad7d99245..0e7480a58012 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -488,12 +488,21 @@ static void bpf_skops_hdr_opt_len(struct sock *sk, struct sk_buff *skb,
 {
 	struct bpf_sock_ops_kern sock_ops;
 	int err;
+	struct tcp_sock *th = (struct tcp_sock *)sk;
 
-	if (likely(!BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk),
+	if (likely(!BPF_SOCK_OPS_TEST_FLAG(th,
 					   BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG)) ||
 	    !*remaining)
 		return;
 
+	if (likely(BPF_SOCK_OPS_TEST_FLAG(th,
+					  BPF_SOCK_OPS_HDR_OPT_LEN_CACHE_CB_FLAG)) &&
+	    th->bpf_opt_len) {
+		*remaining -= th->bpf_opt_len;
+		opts->bpf_opt_len = th->bpf_opt_len;
+		return;
+	}
+
 	/* *remaining has already been aligned to 4 bytes, so *remaining >= 4 */
 
 	/* init sock_ops */
@@ -538,6 +547,7 @@ static void bpf_skops_hdr_opt_len(struct sock *sk, struct sk_buff *skb,
 	opts->bpf_opt_len = *remaining - sock_ops.remaining_opt_len;
 	/* round up to 4 bytes */
 	opts->bpf_opt_len = (opts->bpf_opt_len + 3) & ~3;
+	th->bpf_opt_len = opts->bpf_opt_len;
 
 	*remaining -= opts->bpf_opt_len;
 }
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 90706a47f6ff..f2092de1f432 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -6892,8 +6892,14 @@ enum {
 	 * options first before the BPF program does.
 	 */
 	BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG = (1<<6),
+	/* Fast path to reserve space in a skb under
+	 * sock_ops->op == BPF_SOCK_OPS_HDR_OPT_LEN_CB.
+	 * opt length doesn't change often, so it can save in the tcp_sock. And
+	 * set BPF_SOCK_OPS_HDR_OPT_LEN_CACHE_CB_FLAG to no bpf call.
+	 */
+	BPF_SOCK_OPS_HDR_OPT_LEN_CACHE_CB_FLAG = (1<<7),
 /* Mask of all currently supported cb flags */
-	BPF_SOCK_OPS_ALL_CB_FLAGS       = 0x7F,
+	BPF_SOCK_OPS_ALL_CB_FLAGS       = 0xFF,
 };
 
 /* List of known BPF sock_ops operators.
-- 
2.30.2