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tcp: remove thin_dupack feature

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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: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Yuchung Cheng 2017-01-12 22:11:41 -08:00 committed by David S. Miller
parent ac229dca7e
commit 4a7f600944
5 changed files with 3 additions and 37 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
Documentation/networking/ip-sysctl.txt
View File

@ -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

2
include/linux/tcp.h
View File

@ -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;

7
net/ipv4/sysctl_net_ipv4.c
View File

@ -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,

6
net/ipv4/tcp.c
View File

@ -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:

13
net/ipv4/tcp_input.c
View File

@ -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;
}