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Commit dcb8c9b4 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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tcp_bbr: better deal with suboptimal GSO (II) 



This is second part of dealing with suboptimal device gso parameters.
In first patch (350c9f48 "tcp_bbr: better deal with suboptimal GSO")
we dealt with devices having low gso_max_segs

Some devices lower gso_max_size from 64KB to 16 KB (r8152 is an example)

In order to probe an optimal cwnd, we want BBR being not sensitive
to whatever GSO constraint a device can have.

This patch removes tso_segs_goal() CC callback in favor of
min_tso_segs() for CC wanting to override sysctl_tcp_min_tso_segs

Next patch will remove bbr->tso_segs_goal since it does not have
to be persistent.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Acked-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 7797dc41

include/net/tcp.h

+2 −4
Original line number Diff line number Diff line
@@ -511,8 +511,6 @@ __u32 cookie_v6_init_sequence(const struct sk_buff *skb, __u16 *mss); 
#endif

/* tcp_output.c */



u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,

		     int min_tso_segs);

void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,

			       int nonagle);

int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs);
@@ -981,8 +979,8 @@ struct tcp_congestion_ops { 
	u32  (*undo_cwnd)(struct sock *sk);

	/* hook for packet ack accounting (optional) */

	void (*pkts_acked)(struct sock *sk, const struct ack_sample *sample);

	/* suggest number of segments for each skb to transmit (optional) */

	u32 (*tso_segs_goal)(struct sock *sk);

	/* override sysctl_tcp_min_tso_segs */

	u32 (*min_tso_segs)(struct sock *sk);

	/* returns the multiplier used in tcp_sndbuf_expand (optional) */

	u32 (*sndbuf_expand)(struct sock *sk);

	/* call when packets are delivered to update cwnd and pacing rate,

net/ipv4/tcp_bbr.c

+13 −10
Original line number Diff line number Diff line
@@ -261,23 +261,26 @@ static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain) 
		sk->sk_pacing_rate = rate;

}



/* Return count of segments we want in the skbs we send, or 0 for default. */

static u32 bbr_tso_segs_goal(struct sock *sk)

/* override sysctl_tcp_min_tso_segs */

static u32 bbr_min_tso_segs(struct sock *sk)

{

	struct bbr *bbr = inet_csk_ca(sk);



	return bbr->tso_segs_goal;

	return sk->sk_pacing_rate < (bbr_min_tso_rate >> 3) ? 1 : 2;

}



static void bbr_set_tso_segs_goal(struct sock *sk)

{

	struct tcp_sock *tp = tcp_sk(sk);

	struct bbr *bbr = inet_csk_ca(sk);

	u32 min_segs;

	u32 segs, bytes;



	/* Sort of tcp_tso_autosize() but ignoring

	 * driver provided sk_gso_max_size.

	 */

	bytes = min_t(u32, sk->sk_pacing_rate >> sk->sk_pacing_shift,

		      GSO_MAX_SIZE - 1 - MAX_TCP_HEADER);

	segs = max_t(u32, bytes / tp->mss_cache, bbr_min_tso_segs(sk));



	min_segs = sk->sk_pacing_rate < (bbr_min_tso_rate >> 3) ? 1 : 2;

	bbr->tso_segs_goal = min(tcp_tso_autosize(sk, tp->mss_cache, min_segs),

				 0x7FU);

	bbr->tso_segs_goal = min(segs, 0x7FU);

}



/* Save "last known good" cwnd so we can restore it after losses or PROBE_RTT */
@@ -936,7 +939,7 @@ 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_goal	= bbr_tso_segs_goal,

	.min_tso_segs	= bbr_min_tso_segs,

	.get_info	= bbr_get_info,

	.set_state	= bbr_set_state,

};

net/ipv4/tcp_output.c

+8 −7
Original line number Diff line number Diff line
@@ -1703,7 +1703,7 @@ static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp, 
/* Return how many segs we'd like on a TSO packet,

 * to send one TSO packet per ms

 */

u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,

static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,

			    int min_tso_segs)

{

	u32 bytes, segs;
@@ -1720,7 +1720,6 @@ u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now, 


	return segs;

}

EXPORT_SYMBOL(tcp_tso_autosize);



/* Return the number of segments we want in the skb we are transmitting.

 * See if congestion control module wants to decide; otherwise, autosize.
@@ -1728,11 +1727,13 @@ EXPORT_SYMBOL(tcp_tso_autosize); 
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 = ca_ops->tso_segs_goal ? ca_ops->tso_segs_goal(sk) : 0;

	u32 min_tso, tso_segs;



	if (!tso_segs)

		tso_segs = 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);

}