Revert "net-tcp: re-generalize TSO sizing in TCP CC module API"

This reverts commit 39d3633.
xanmod · Aug 3, 2022 · 5ef85db · 5ef85db
1 parent 4cd1891
commit 5ef85db
Show file tree

Hide file tree

Showing 4 changed files with 21 additions and 34 deletions.
diff --git a/include/net/tcp.h b/include/net/tcp.h
@@ -1077,8 +1077,8 @@ struct tcp_congestion_ops {
 	/* hook for packet ack accounting (optional) */
 	void (*pkts_acked)(struct sock *sk, const struct ack_sample *sample);
 
-	/* pick target number of segments per TSO/GSO skb (optional): */
-	u32 (*tso_segs)(struct sock *sk, unsigned int mss_now);
+	/* override sysctl_tcp_min_tso_segs */
+	u32 (*min_tso_segs)(struct sock *sk);
 
 	/* react to a specific lost skb (optional) */
 	void (*skb_marked_lost)(struct sock *sk, const struct sk_buff *skb);

diff --git a/net/ipv4/bpf_tcp_ca.c b/net/ipv4/bpf_tcp_ca.c
@@ -20,7 +20,7 @@ static u32 optional_ops[] = {
 	offsetof(struct tcp_congestion_ops, cwnd_event),
 	offsetof(struct tcp_congestion_ops, in_ack_event),
 	offsetof(struct tcp_congestion_ops, pkts_acked),
-	offsetof(struct tcp_congestion_ops, tso_segs),
+	offsetof(struct tcp_congestion_ops, min_tso_segs),
 	offsetof(struct tcp_congestion_ops, sndbuf_expand),
 	offsetof(struct tcp_congestion_ops, cong_control),
 };

diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c
@@ -292,40 +292,26 @@ static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain)
 		sk->sk_pacing_rate = rate;
 }
 
+/* override sysctl_tcp_min_tso_segs */
 static u32 bbr_min_tso_segs(struct sock *sk)
 {
 	return sk->sk_pacing_rate < (bbr_min_tso_rate >> 3) ? 1 : 2;
 }
 
-/* Return the number of segments BBR would like in a TSO/GSO skb, given
- * a particular max gso size as a constraint.
- */
-static u32 bbr_tso_segs_generic(struct sock *sk, unsigned int mss_now,
-				u32 gso_max_size)
-{
-	u32 segs;
-	u64 bytes;
-
-	/* Budget a TSO/GSO burst size allowance based on bw (pacing_rate). */
-	bytes = sk->sk_pacing_rate >> sk->sk_pacing_shift;
-
-	bytes = min_t(u32, bytes, gso_max_size - 1 - MAX_TCP_HEADER);
-	segs = max_t(u32, bytes / mss_now, bbr_min_tso_segs(sk));
-	return segs;
-}
-
-/* Custom tcp_tso_autosize() for BBR, used at transmit time to cap skb size. */
-static u32  bbr_tso_segs(struct sock *sk, unsigned int mss_now)
-{
-	return bbr_tso_segs_generic(sk, mss_now, sk->sk_gso_max_size);
-}
-
-/* Like bbr_tso_segs(), using mss_cache, ignoring driver's sk_gso_max_size. */
 static u32 bbr_tso_segs_goal(struct sock *sk)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
+	u32 segs, bytes;
+
+	/* Sort of tcp_tso_autosize() but ignoring
+	 * driver provided sk_gso_max_size.
+	 */
+	bytes = min_t(unsigned long,
+		      sk->sk_pacing_rate >> READ_ONCE(sk->sk_pacing_shift),
+		      GSO_MAX_SIZE - 1 - MAX_TCP_HEADER);
+	segs = max_t(u32, bytes / tp->mss_cache, bbr_min_tso_segs(sk));
 
-	return  bbr_tso_segs_generic(sk, tp->mss_cache, GSO_MAX_SIZE);
+	return min(segs, 0x7FU);
 }
 
 /* Save "last known good" cwnd so we can restore it after losses or PROBE_RTT */
@@ -1161,7 +1147,7 @@ static struct tcp_congestion_ops tcp_bbr_cong_ops __read_mostly = {
 	.undo_cwnd	= bbr_undo_cwnd,
 	.cwnd_event	= bbr_cwnd_event,
 	.ssthresh	= bbr_ssthresh,
-	.tso_segs	= bbr_tso_segs,
+	.min_tso_segs	= bbr_min_tso_segs,
 	.get_info	= bbr_get_info,
 	.set_state	= bbr_set_state,
 };

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
@@ -1993,12 +1993,13 @@ static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
 static u32 tcp_tso_segs(struct sock *sk, unsigned int mss_now)
 {
 	const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
-	u32 tso_segs;
+	u32 min_tso, tso_segs;
 
-	tso_segs = ca_ops->tso_segs ?
-		ca_ops->tso_segs(sk, mss_now) :
-		tcp_tso_autosize(sk, mss_now,
-				 sock_net(sk)->ipv4.sysctl_tcp_min_tso_segs);
+	min_tso = ca_ops->min_tso_segs ?
+			ca_ops->min_tso_segs(sk) :
+			sock_net(sk)->ipv4.sysctl_tcp_min_tso_segs;
+
+	tso_segs = tcp_tso_autosize(sk, mss_now, min_tso);
 	return min_t(u32, tso_segs, sk->sk_gso_max_segs);
 }