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Message-ID: <20250613230907.1702265-3-ncardwell.sw@gmail.com>
Date: Fri, 13 Jun 2025 19:09:05 -0400
From: Neal Cardwell <ncardwell.sw@...il.com>
To: David Miller <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Eric Dumazet <edumazet@...gle.com>
Cc: netdev@...r.kernel.org,
Neal Cardwell <ncardwell@...gle.com>,
Yuchung Cheng <ycheng@...gle.com>
Subject: [PATCH net-next 2/3] tcp: remove RFC3517/RFC6675 hint state: lost_skb_hint, lost_cnt_hint
From: Neal Cardwell <ncardwell@...gle.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 <ycheng@...gle.com>
Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
Reviewed-by: Yuchung Cheng <ycheng@...gle.com>
Reviewed-by: Eric Dumazet <edumazet@...gle.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 | 15 ---------------
net/ipv4/tcp_output.c | 5 -----
6 files changed, 1 insertion(+), 28 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 b52eaa45e652f..9ded9b371d98a 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;
@@ -3319,8 +3307,6 @@ 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);
}
@@ -3385,7 +3371,6 @@ static int tcp_clean_rtx_queue(struct sock *sk, const struct sk_buff *ack_skb,
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
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