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Commit 3cfe3baa authored by Ilpo Järvinen's avatar Ilpo Järvinen Committed by David S. Miller
Browse files

[TCP]: Add two new spurious RTO responses to FRTO 



New sysctl tcp_frto_response is added to select amongst these
responses:
	- Rate halving based; reuses CA_CWR state (default)
	- Very conservative; used to be the only one available (=1)
	- Undo cwr; undoes ssthresh and cwnd reductions (=2)

The response with rate halving requires a new parameter to
tcp_enter_cwr because FRTO has already reduced ssthresh and
doing a second reduction there has to be prevented. In addition,
to keep things nice on 80 cols screen, a local variable was
added.

Signed-off-by: default avatarIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent c5e7af0d

include/linux/sysctl.h

+1 −0
Original line number Diff line number Diff line
@@ -439,6 +439,7 @@ enum 
	NET_TCP_AVAIL_CONG_CONTROL=122,

	NET_TCP_ALLOWED_CONG_CONTROL=123,

	NET_TCP_MAX_SSTHRESH=124,

	NET_TCP_FRTO_RESPONSE=125,

};



enum {

include/net/tcp.h

+2 −1
Original line number Diff line number Diff line
@@ -220,6 +220,7 @@ extern int sysctl_tcp_app_win; 
extern int sysctl_tcp_adv_win_scale;

extern int sysctl_tcp_tw_reuse;

extern int sysctl_tcp_frto;

extern int sysctl_tcp_frto_response;

extern int sysctl_tcp_low_latency;

extern int sysctl_tcp_dma_copybreak;

extern int sysctl_tcp_nometrics_save;
@@ -738,7 +739,7 @@ static inline void tcp_sync_left_out(struct tcp_sock *tp) 
	tp->left_out = tp->sacked_out + tp->lost_out;

}



extern void tcp_enter_cwr(struct sock *sk);

extern void tcp_enter_cwr(struct sock *sk, const int set_ssthresh);

extern __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst);



/* Slow start with delack produces 3 packets of burst, so that

net/ipv4/sysctl_net_ipv4.c

+8 −0
Original line number Diff line number Diff line
@@ -646,6 +646,14 @@ ctl_table ipv4_table[] = { 
		.mode		= 0644,

		.proc_handler	= &proc_dointvec

	},

	{

		.ctl_name	= NET_TCP_FRTO_RESPONSE,

		.procname	= "tcp_frto_response",

		.data		= &sysctl_tcp_frto_response,

		.maxlen		= sizeof(int),

		.mode		= 0644,

		.proc_handler	= &proc_dointvec

	},

	{

		.ctl_name	= NET_TCP_LOW_LATENCY,

		.procname	= "tcp_low_latency",

net/ipv4/tcp_input.c

+32 −4
Original line number Diff line number Diff line
@@ -86,6 +86,7 @@ int sysctl_tcp_stdurg __read_mostly; 
int sysctl_tcp_rfc1337 __read_mostly;

int sysctl_tcp_max_orphans __read_mostly = NR_FILE;

int sysctl_tcp_frto __read_mostly;

int sysctl_tcp_frto_response __read_mostly;

int sysctl_tcp_nometrics_save __read_mostly;



int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
@@ -762,15 +763,17 @@ __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst) 
}



/* Set slow start threshold and cwnd not falling to slow start */

void tcp_enter_cwr(struct sock *sk)

void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)

{

	struct tcp_sock *tp = tcp_sk(sk);

	const struct inet_connection_sock *icsk = inet_csk(sk);



	tp->prior_ssthresh = 0;

	tp->bytes_acked = 0;

	if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {

		tp->undo_marker = 0;

		tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);

		if (set_ssthresh)

			tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);

		tp->snd_cwnd = min(tp->snd_cwnd,

				   tcp_packets_in_flight(tp) + 1U);

		tp->snd_cwnd_cnt = 0;
@@ -2003,7 +2006,7 @@ static void tcp_try_to_open(struct sock *sk, struct tcp_sock *tp, int flag) 
		tp->retrans_stamp = 0;



	if (flag&FLAG_ECE)

		tcp_enter_cwr(sk);

		tcp_enter_cwr(sk, 1);



	if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {

		int state = TCP_CA_Open;
@@ -2579,6 +2582,21 @@ static void tcp_conservative_spur_to_response(struct tcp_sock *tp) 
	tcp_moderate_cwnd(tp);

}



/* A conservative spurious RTO response algorithm: reduce cwnd using

 * rate halving and continue in congestion avoidance.

 */

static void tcp_ratehalving_spur_to_response(struct sock *sk)

{

	struct tcp_sock *tp = tcp_sk(sk);

	tcp_enter_cwr(sk, 0);

	tp->high_seq = tp->frto_highmark; 	/* Smoother w/o this? - ij */

}



static void tcp_undo_spur_to_response(struct sock *sk)

{

	tcp_undo_cwr(sk, 1);

}



/* F-RTO spurious RTO detection algorithm (RFC4138)

 *

 * F-RTO affects during two new ACKs following RTO (well, almost, see inline
@@ -2661,7 +2679,17 @@ static int tcp_process_frto(struct sock *sk, u32 prior_snd_una, int flag) 
		tp->frto_counter = 2;

		return 1;

	} else /* frto_counter == 2 */ {

		switch (sysctl_tcp_frto_response) {

		case 2:

			tcp_undo_spur_to_response(sk);

			break;

		case 1:

			tcp_conservative_spur_to_response(tp);

			break;

		default:

			tcp_ratehalving_spur_to_response(sk);

			break;

		};

		tp->frto_counter = 0;

	}

	return 0;

net/ipv4/tcp_output.c

+1 −1
Original line number Diff line number Diff line
@@ -545,7 +545,7 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it, 
	if (likely(err <= 0))

		return err;



	tcp_enter_cwr(sk);

	tcp_enter_cwr(sk, 1);



	return net_xmit_eval(err);