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SubjectRe: [net-next PATCH v5 3/3] net: TCP thin dupack
On Thu, 18 Feb 2010, Andreas Petlund wrote:

> This patch enables fast retransmissions after one dupACK for
> TCP if the stream is identified as thin. This will reduce
> latencies for thin streams that are not able to trigger fast
> retransmissions due to high packet interarrival time. This
> mechanism is only active if enabled by iocontrol or syscontrol
> and the stream is identified as thin.
>
>
> Signed-off-by: Andreas Petlund <apetlund@simula.no>
> ---
> Documentation/networking/ip-sysctl.txt | 12 ++++++++++++
> include/linux/tcp.h | 4 +++-
> include/net/tcp.h | 1 +
> net/ipv4/sysctl_net_ipv4.c | 7 +++++++
> net/ipv4/tcp.c | 7 +++++++
> net/ipv4/tcp_input.c | 12 ++++++++++++
> 6 files changed, 42 insertions(+), 1 deletions(-)
>
> diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
> index f147310..2571a62 100644
> --- a/Documentation/networking/ip-sysctl.txt
> +++ b/Documentation/networking/ip-sysctl.txt
> @@ -499,6 +499,18 @@ 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
> +
> UDP variables:
>
> udp_mem - vector of 3 INTEGERs: min, pressure, max
> diff --git a/include/linux/tcp.h b/include/linux/tcp.h
> index 3ba8b07..a778ee0 100644
> --- a/include/linux/tcp.h
> +++ b/include/linux/tcp.h
> @@ -104,6 +104,7 @@ enum {
> #define TCP_MD5SIG 14 /* TCP MD5 Signature (RFC2385) */
> #define TCP_COOKIE_TRANSACTIONS 15 /* TCP Cookie Transactions */
> #define TCP_THIN_LINEAR_TIMEOUTS 16 /* Use linear timeouts for thin streams*/
> +#define TCP_THIN_DUPACK 17 /* Fast retrans. after 1 dupack */
>
> /* for TCP_INFO socket option */
> #define TCPI_OPT_TIMESTAMPS 1
> @@ -343,7 +344,8 @@ struct tcp_sock {
> u8 frto_counter; /* Number of new acks after RTO */
> u8 nonagle : 4,/* Disable Nagle algorithm? */
> thin_lto : 1,/* Use linear timeouts for thin streams */
> - unused : 3;
> + thin_dupack : 1,/* Fast retransmit on first dupack */
> + unused : 2;
>
> /* RTT measurement */
> u32 srtt; /* smoothed round trip time << 3 */
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 6278fc7..56f0aec 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -245,6 +245,7 @@ extern int sysctl_tcp_slow_start_after_idle;
> extern int sysctl_tcp_max_ssthresh;
> extern int sysctl_tcp_cookie_size;
> extern int sysctl_tcp_thin_linear_timeouts;
> +extern int sysctl_tcp_thin_dupack;
>
> extern atomic_t tcp_memory_allocated;
> extern struct percpu_counter tcp_sockets_allocated;
> diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
> index e6a2460..c1bc074 100644
> --- a/net/ipv4/sysctl_net_ipv4.c
> +++ b/net/ipv4/sysctl_net_ipv4.c
> @@ -582,6 +582,13 @@ 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 = "udp_mem",
> .data = &sysctl_udp_mem,
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 21bae9a..5901010 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -2236,6 +2236,13 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
> tp->thin_lto = val;
> break;
>
> + case TCP_THIN_DUPACK:
> + if (val < 0 || val > 1)
> + err = -EINVAL;
> + else
> + tp->thin_dupack = val;
> + break;
> +
> case TCP_CORK:
> /* When set indicates to always queue non-full frames.
> * Later the user clears this option and we transmit
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 3fddc69..8d950b9 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -89,6 +89,8 @@ int sysctl_tcp_frto __read_mostly = 2;
> int sysctl_tcp_frto_response __read_mostly;
> int sysctl_tcp_nometrics_save __read_mostly;
>
> +int sysctl_tcp_thin_dupack __read_mostly;
> +
> int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
> int sysctl_tcp_abc __read_mostly;
>
> @@ -2447,6 +2449,16 @@ static int tcp_time_to_recover(struct sock *sk)
> return 1;
> }
>
> + /* 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) && sk->sk_send_head == NULL)

Use tcp_send_head(sk) instead.

> + return 1;
> +
> return 0;
> }

Other than that,

Acked-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>

--
i.
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