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Commit 4a7f6009 authored by Yuchung Cheng's avatar Yuchung Cheng Committed by David S. Miller
Browse files

tcp: remove thin_dupack feature 



Thin stream DUPACK is to start fast recovery on only one DUPACK
provided the connection is a thin stream (i.e., low inflight).  But
this older feature is now subsumed with RACK. If a connection
receives only a single DUPACK, RACK would arm a reordering timer
and soon starts fast recovery instead of timeout if no further
ACKs are received.

The socket option (THIN_DUPACK) is kept as a nop for compatibility.
Note that this patch does not change another thin-stream feature
which enables linear RTO. Although it might be good to generalize
that in the future (i.e., linear RTO for the first say 3 retries).

Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
Acked-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent ac229dca

Documentation/networking/ip-sysctl.txt

+0 −12
Original line number Diff line number Diff line
@@ -703,18 +703,6 @@ tcp_thin_linear_timeouts - BOOLEAN 
	Documentation/networking/tcp-thin.txt

	Default: 0



tcp_thin_dupack - BOOLEAN

	Enable dynamic triggering of retransmissions after one dupACK

	for thin streams. If set, a check is performed upon reception

	of a dupACK to determine if the stream is thin (less than 4

	packets in flight). As long as the stream is found to be thin,

	data is retransmitted on the first received dupACK. This

	improves retransmission latency for non-aggressive thin

	streams, often found to be time-dependent.

	For more information on thin streams, see

	Documentation/networking/tcp-thin.txt

	Default: 0



tcp_limit_output_bytes - INTEGER

	Controls TCP Small Queue limit per tcp socket.

	TCP bulk sender tends to increase packets in flight until it

include/linux/tcp.h

+1 −1
Original line number Diff line number Diff line
@@ -220,7 +220,7 @@ struct tcp_sock { 
		unused:5;

	u8	nonagle     : 4,/* Disable Nagle algorithm?             */

		thin_lto    : 1,/* Use linear timeouts for thin streams */

		thin_dupack : 1,/* Fast retransmit on first dupack      */

		unused1	    : 1,

		repair      : 1,

		frto        : 1;/* F-RTO (RFC5682) activated in CA_Loss */

	u8	repair_queue;

net/ipv4/sysctl_net_ipv4.c

+0 −7
Original line number Diff line number Diff line
@@ -536,13 +536,6 @@ static struct ctl_table ipv4_table[] = { 
		.mode           = 0644,

		.proc_handler   = proc_dointvec

	},

	{

		.procname       = "tcp_thin_dupack",

		.data           = &sysctl_tcp_thin_dupack,

		.maxlen         = sizeof(int),

		.mode           = 0644,

		.proc_handler   = proc_dointvec

	},

	{

		.procname	= "tcp_early_retrans",

		.data		= &sysctl_tcp_early_retrans,

net/ipv4/tcp.c

+2 −4
Original line number Diff line number Diff line
@@ -2474,9 +2474,6 @@ static int do_tcp_setsockopt(struct sock *sk, int level, 
	case TCP_THIN_DUPACK:

		if (val < 0 || val > 1)

			err = -EINVAL;

		else {

			tp->thin_dupack = val;

		}

		break;



	case TCP_REPAIR:
@@ -2966,8 +2963,9 @@ static int do_tcp_getsockopt(struct sock *sk, int level, 
	case TCP_THIN_LINEAR_TIMEOUTS:

		val = tp->thin_lto;

		break;



	case TCP_THIN_DUPACK:

		val = tp->thin_dupack;

		val = 0;

		break;



	case TCP_REPAIR:

net/ipv4/tcp_input.c

+0 −13
Original line number Diff line number Diff line
@@ -95,9 +95,6 @@ int sysctl_tcp_rfc1337 __read_mostly; 
int sysctl_tcp_max_orphans __read_mostly = NR_FILE;

int sysctl_tcp_frto __read_mostly = 2;

int sysctl_tcp_min_rtt_wlen __read_mostly = 300;



int sysctl_tcp_thin_dupack __read_mostly;



int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;

int sysctl_tcp_early_retrans __read_mostly = 3;

int sysctl_tcp_invalid_ratelimit __read_mostly = HZ/2;
@@ -2170,16 +2167,6 @@ static bool tcp_time_to_recover(struct sock *sk, int flag) 
	if (tcp_dupack_heuristics(tp) > tp->reordering)

		return true;



	/* If a thin stream is detected, retransmit after first

	 * received dupack. Employ only if SACK is supported in order

	 * to avoid possible corner-case series of spurious retransmissions

	 * Use only if there are no unsent data.

	 */

	if ((tp->thin_dupack || sysctl_tcp_thin_dupack) &&

	    tcp_stream_is_thin(tp) && tcp_dupack_heuristics(tp) > 1 &&

	    tcp_is_sack(tp) && !tcp_send_head(sk))

		return true;



	return false;

}