[PATCH net-next v2 2/3] tcp: remove RFC3517/RFC6675 hint state: lost_skb_hint, lost_cnt_hint
From: Neal Cardwell <hidden>
Date: 2025-06-15 00:14:44
Subsystem:
documentation, networking [general], networking [tcp], the rest · Maintainers:
Jonathan Corbet, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Neal Cardwell, Linus Torvalds
From: Neal Cardwell <ncardwell@google.com> Now that obsolete RFC3517/RFC6675 TCP loss detection has been removed, we can remove the somewhat complex and intrusive code to maintain its hint state: lost_skb_hint and lost_cnt_hint. This commit makes tcp_clear_retrans_hints_partial() empty. We will remove tcp_clear_retrans_hints_partial() and its call sites in the next commit. Suggested-by: Yuchung Cheng <redacted> Signed-off-by: Neal Cardwell <ncardwell@google.com> Reviewed-by: Yuchung Cheng <redacted> Reviewed-by: Eric Dumazet <edumazet@google.com> --- .../networking/net_cachelines/tcp_sock.rst | 2 -- include/linux/tcp.h | 3 --- include/net/tcp.h | 1 - net/ipv4/tcp.c | 3 +-- net/ipv4/tcp_input.c | 19 ------------------- net/ipv4/tcp_output.c | 5 ----- 6 files changed, 1 insertion(+), 32 deletions(-)
diff --git a/Documentation/networking/net_cachelines/tcp_sock.rst b/Documentation/networking/net_cachelines/tcp_sock.rst
index bc9b2131bf7ac..7bbda5944ee2f 100644
--- a/Documentation/networking/net_cachelines/tcp_sock.rst
+++ b/Documentation/networking/net_cachelines/tcp_sock.rst@@ -115,7 +115,6 @@ u32 lost_out read_mostly read_m u32 sacked_out read_mostly read_mostly tcp_left_out(tx);tcp_packets_in_flight(tx/rx);tcp_clean_rtx_queue(rx) struct hrtimer pacing_timer struct hrtimer compressed_ack_timer -struct sk_buff* lost_skb_hint read_mostly tcp_clean_rtx_queue struct sk_buff* retransmit_skb_hint read_mostly tcp_clean_rtx_queue struct rb_root out_of_order_queue read_mostly tcp_data_queue,tcp_fast_path_check struct sk_buff* ooo_last_skb
@@ -123,7 +122,6 @@ struct tcp_sack_block[1] duplicate_sack struct tcp_sack_block[4] selective_acks struct tcp_sack_block[4] recv_sack_cache struct sk_buff* highest_sack read_write tcp_event_new_data_sent -int lost_cnt_hint u32 prior_ssthresh u32 high_seq u32 retrans_stamp
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 29f59d50dc73f..1a5737b3753d0 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h@@ -208,7 +208,6 @@ struct tcp_sock { u32 notsent_lowat; /* TCP_NOTSENT_LOWAT */ u16 gso_segs; /* Max number of segs per GSO packet */ /* from STCP, retrans queue hinting */ - struct sk_buff *lost_skb_hint; struct sk_buff *retransmit_skb_hint; __cacheline_group_end(tcp_sock_read_tx);
@@ -419,8 +418,6 @@ struct tcp_sock { struct tcp_sack_block recv_sack_cache[4]; - int lost_cnt_hint; - u32 prior_ssthresh; /* ssthresh saved at recovery start */ u32 high_seq; /* snd_nxt at onset of congestion */
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 5078ad868feef..f57d121837949 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h@@ -1813,7 +1813,6 @@ static inline void tcp_mib_init(struct net *net) /* from STCP */ static inline void tcp_clear_retrans_hints_partial(struct tcp_sock *tp) { - tp->lost_skb_hint = NULL; } static inline void tcp_clear_all_retrans_hints(struct tcp_sock *tp)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index f64f8276a73cd..27d3ef83ce7b2 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c@@ -5053,9 +5053,8 @@ static void __init tcp_struct_check(void) CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_read_tx, reordering); CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_read_tx, notsent_lowat); CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_read_tx, gso_segs); - CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_read_tx, lost_skb_hint); CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_read_tx, retransmit_skb_hint); - CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_read_tx, 40); + CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_read_tx, 32); /* TXRX read-mostly hotpath cache lines */ CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_read_txrx, tsoffset);
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index dc234d3854aa4..e8e130e946f14 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c@@ -1451,11 +1451,6 @@ static u8 tcp_sacktag_one(struct sock *sk, tp->sacked_out += pcount; /* Out-of-order packets delivered */ state->sack_delivered += pcount; - - /* Lost marker hint past SACKed? Tweak RFC3517 cnt */ - if (tp->lost_skb_hint && - before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq)) - tp->lost_cnt_hint += pcount; } /* D-SACK. We can detect redundant retransmission in S|R and plain R
@@ -1496,9 +1491,6 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev, tcp_skb_timestamp_us(skb)); tcp_rate_skb_delivered(sk, skb, state->rate); - if (skb == tp->lost_skb_hint) - tp->lost_cnt_hint += pcount; - TCP_SKB_CB(prev)->end_seq += shifted; TCP_SKB_CB(skb)->seq += shifted;
@@ -1531,10 +1523,6 @@ static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev, if (skb == tp->retransmit_skb_hint) tp->retransmit_skb_hint = prev; - if (skb == tp->lost_skb_hint) { - tp->lost_skb_hint = prev; - tp->lost_cnt_hint -= tcp_skb_pcount(prev); - } TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags; TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor;
@@ -3318,8 +3306,6 @@ static int tcp_clean_rtx_queue(struct sock *sk, const struct sk_buff *ack_skb, next = skb_rb_next(skb); if (unlikely(skb == tp->retransmit_skb_hint)) tp->retransmit_skb_hint = NULL; - if (unlikely(skb == tp->lost_skb_hint)) - tp->lost_skb_hint = NULL; tcp_highest_sack_replace(sk, skb, next); tcp_rtx_queue_unlink_and_free(skb, sk); }
@@ -3377,14 +3363,9 @@ static int tcp_clean_rtx_queue(struct sock *sk, const struct sk_buff *ack_skb, if (flag & FLAG_RETRANS_DATA_ACKED) flag &= ~FLAG_ORIG_SACK_ACKED; } else { - int delta; - /* Non-retransmitted hole got filled? That's reordering */ if (before(reord, prior_fack)) tcp_check_sack_reordering(sk, reord, 0); - - delta = prior_sacked - tp->sacked_out; - tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta); } } else if (skb && rtt_update && sack_rtt_us >= 0 && sack_rtt_us > tcp_stamp_us_delta(tp->tcp_mstamp,
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 3ac8d2d17e1ff..b0ffefe604b4c 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c@@ -1554,11 +1554,6 @@ static void tcp_adjust_pcount(struct sock *sk, const struct sk_buff *skb, int de if (tcp_is_reno(tp) && decr > 0) tp->sacked_out -= min_t(u32, tp->sacked_out, decr); - if (tp->lost_skb_hint && - before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(tp->lost_skb_hint)->seq) && - (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) - tp->lost_cnt_hint -= decr; - tcp_verify_left_out(tp); }
--
2.50.0.rc1.591.g9c95f17f64-goog