Commit bcc843bb authored by Jakub Kicinski's avatar Jakub Kicinski
Browse files

Merge branch 'tcp-fix-receive-autotune-again' 

Matthieu Baerts says:

====================
tcp: fix receive autotune again

Neal Cardwell found that recent kernels were having RWIN limited
issues, even when net.ipv4.tcp_rmem[2] was set to a very big value like
512MB.

He suspected that tcp_stream default buffer size (64KB) was triggering
heuristic added in ea33537d ("tcp: add receive queue awareness
in tcp_rcv_space_adjust()").

After more testing, it turns out the bug was added earlier
with commit 65c52878 ("tcp: fix sk_rcvbuf overshoot").

I forgot once again that DRS has one RTT latency.

MPTCP also got the same issue.

This series :
 - Prevents calling tcp_rcvbuf_grow() on some MPTCP subflows.
 - adds rcv_ssthresh, window_clamp and rcv_wnd to trace_tcp_rcvbuf_grow().
 - Refactors code in a patch with no functional changes.
 - Fixes the issue in the final patch.
====================

Link: https://patch.msgid.link/20251028-net-tcp-recv-autotune-v3-0-74b43ba4c84c@kernel.org


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parents f99c5792 aa251c84

include/net/tcp.h

+1 −1
Original line number Diff line number Diff line
@@ -370,7 +370,7 @@ void tcp_delack_timer_handler(struct sock *sk); 
int tcp_ioctl(struct sock *sk, int cmd, int *karg);

enum skb_drop_reason tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb);

void tcp_rcv_established(struct sock *sk, struct sk_buff *skb);

void tcp_rcvbuf_grow(struct sock *sk);

void tcp_rcvbuf_grow(struct sock *sk, u32 newval);

void tcp_rcv_space_adjust(struct sock *sk);

int tcp_twsk_unique(struct sock *sk, struct sock *sktw, void *twp);

void tcp_twsk_destructor(struct sock *sk);

include/trace/events/tcp.h

+9 −0
Original line number Diff line number Diff line
@@ -218,6 +218,9 @@ TRACE_EVENT(tcp_rcvbuf_grow, 
		__field(__u32, space)

		__field(__u32, ooo_space)

		__field(__u32, rcvbuf)

		__field(__u32, rcv_ssthresh)

		__field(__u32, window_clamp)

		__field(__u32, rcv_wnd)

		__field(__u8, scaling_ratio)

		__field(__u16, sport)

		__field(__u16, dport)
@@ -245,6 +248,9 @@ TRACE_EVENT(tcp_rcvbuf_grow, 
				     tp->rcv_nxt;



		__entry->rcvbuf = sk->sk_rcvbuf;

		__entry->rcv_ssthresh = tp->rcv_ssthresh;

		__entry->window_clamp = tp->window_clamp;

		__entry->rcv_wnd = tp->rcv_wnd;

		__entry->scaling_ratio = tp->scaling_ratio;

		__entry->sport = ntohs(inet->inet_sport);

		__entry->dport = ntohs(inet->inet_dport);
@@ -264,11 +270,14 @@ TRACE_EVENT(tcp_rcvbuf_grow, 
	),



	TP_printk("time=%u rtt_us=%u copied=%u inq=%u space=%u ooo=%u scaling_ratio=%u rcvbuf=%u "

		  "rcv_ssthresh=%u window_clamp=%u rcv_wnd=%u "

		  "family=%s sport=%hu dport=%hu saddr=%pI4 daddr=%pI4 "

		  "saddrv6=%pI6c daddrv6=%pI6c skaddr=%p sock_cookie=%llx",

		  __entry->time, __entry->rtt_us, __entry->copied,

		  __entry->inq, __entry->space, __entry->ooo_space,

		  __entry->scaling_ratio, __entry->rcvbuf,

		  __entry->rcv_ssthresh, __entry->window_clamp,

		  __entry->rcv_wnd,

		  show_family_name(__entry->family),

		  __entry->sport, __entry->dport,

		  __entry->saddr, __entry->daddr,

net/ipv4/tcp_input.c

+14 −7
Original line number Diff line number Diff line
@@ -891,18 +891,27 @@ static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, 
	}

}



void tcp_rcvbuf_grow(struct sock *sk)

void tcp_rcvbuf_grow(struct sock *sk, u32 newval)

{

	const struct net *net = sock_net(sk);

	struct tcp_sock *tp = tcp_sk(sk);

	int rcvwin, rcvbuf, cap;

	u32 rcvwin, rcvbuf, cap, oldval;

	u64 grow;



	oldval = tp->rcvq_space.space;

	tp->rcvq_space.space = newval;



	if (!READ_ONCE(net->ipv4.sysctl_tcp_moderate_rcvbuf) ||

	    (sk->sk_userlocks & SOCK_RCVBUF_LOCK))

		return;



	/* DRS is always one RTT late. */

	rcvwin = newval << 1;



	/* slow start: allow the sender to double its rate. */

	rcvwin = tp->rcvq_space.space << 1;

	grow = (u64)rcvwin * (newval - oldval);

	do_div(grow, oldval);

	rcvwin += grow << 1;



	if (!RB_EMPTY_ROOT(&tp->out_of_order_queue))

		rcvwin += TCP_SKB_CB(tp->ooo_last_skb)->end_seq - tp->rcv_nxt;
@@ -943,9 +952,7 @@ void tcp_rcv_space_adjust(struct sock *sk) 


	trace_tcp_rcvbuf_grow(sk, time);



	tp->rcvq_space.space = copied;



	tcp_rcvbuf_grow(sk);

	tcp_rcvbuf_grow(sk, copied);



new_measure:

	tp->rcvq_space.seq = tp->copied_seq;
@@ -5270,7 +5277,7 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb) 
	}

	/* do not grow rcvbuf for not-yet-accepted or orphaned sockets. */

	if (sk->sk_socket)

		tcp_rcvbuf_grow(sk);

		tcp_rcvbuf_grow(sk, tp->rcvq_space.space);

}



static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb,

net/mptcp/protocol.c

+17 −9
Original line number Diff line number Diff line
@@ -194,17 +194,26 @@ static bool mptcp_ooo_try_coalesce(struct mptcp_sock *msk, struct sk_buff *to, 
 * - mptcp does not maintain a msk-level window clamp

 * - returns true when  the receive buffer is actually updated

 */

static bool mptcp_rcvbuf_grow(struct sock *sk)

static bool mptcp_rcvbuf_grow(struct sock *sk, u32 newval)

{

	struct mptcp_sock *msk = mptcp_sk(sk);

	const struct net *net = sock_net(sk);

	int rcvwin, rcvbuf, cap;

	u32 rcvwin, rcvbuf, cap, oldval;

	u64 grow;



	oldval = msk->rcvq_space.space;

	msk->rcvq_space.space = newval;

	if (!READ_ONCE(net->ipv4.sysctl_tcp_moderate_rcvbuf) ||

	    (sk->sk_userlocks & SOCK_RCVBUF_LOCK))

		return false;



	rcvwin = msk->rcvq_space.space << 1;

	/* DRS is always one RTT late. */

	rcvwin = newval << 1;



	/* slow start: allow the sender to double its rate. */

	grow = (u64)rcvwin * (newval - oldval);

	do_div(grow, oldval);

	rcvwin += grow << 1;



	if (!RB_EMPTY_ROOT(&msk->out_of_order_queue))

		rcvwin += MPTCP_SKB_CB(msk->ooo_last_skb)->end_seq - msk->ack_seq;
@@ -334,7 +343,7 @@ static void mptcp_data_queue_ofo(struct mptcp_sock *msk, struct sk_buff *skb) 
	skb_set_owner_r(skb, sk);

	/* do not grow rcvbuf for not-yet-accepted or orphaned sockets. */

	if (sk->sk_socket)

		mptcp_rcvbuf_grow(sk);

		mptcp_rcvbuf_grow(sk, msk->rcvq_space.space);

}



static void mptcp_init_skb(struct sock *ssk, struct sk_buff *skb, int offset,
@@ -2049,9 +2058,7 @@ static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied) 
	if (msk->rcvq_space.copied <= msk->rcvq_space.space)

		goto new_measure;



	msk->rcvq_space.space = msk->rcvq_space.copied;

	if (mptcp_rcvbuf_grow(sk)) {



	if (mptcp_rcvbuf_grow(sk, msk->rcvq_space.copied)) {

		/* Make subflows follow along.  If we do not do this, we

		 * get drops at subflow level if skbs can't be moved to

		 * the mptcp rx queue fast enough (announced rcv_win can
@@ -2063,8 +2070,9 @@ static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied) 


			ssk = mptcp_subflow_tcp_sock(subflow);

			slow = lock_sock_fast(ssk);

			tcp_sk(ssk)->rcvq_space.space = msk->rcvq_space.copied;

			tcp_rcvbuf_grow(ssk);

			/* subflows can be added before tcp_init_transfer() */

			if (tcp_sk(ssk)->rcvq_space.space)

				tcp_rcvbuf_grow(ssk, msk->rcvq_space.copied);

			unlock_sock_fast(ssk, slow);

		}

	}