netdev - Re: [PATCH] tcp: Increase the initial congestion window to 10.

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Message-ID: <AANLkTimsx4NX01Gc0YKazENqnDVLrG+-iL4=o+yDTRar@mail.gmail.com>
Date:	Thu, 3 Feb 2011 12:28:03 -0800
From:	Yuchung Cheng <ycheng@...gle.com>
To:	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] tcp: Increase the initial congestion window to 10.

Thanks for doing this!

Acked-by: Yuchung Cheng <ycheng@...gle.com>

On Wed, Feb 2, 2011 at 5:07 PM, David Miller <davem@...emloft.net> wrote:
>
> Signed-off-by: David S. Miller <davem@...emloft.net>
> ---
>
> I've left the DCCP code to keep using RFC3390 logic, if they
> wish to adopt this change in their code they can do so by
> simply deleting the rfc33390_bytes_to_packets() function and
> using TCP_INIT_CWND in their assignment.
>
>  include/net/tcp.h      |   12 +++---------
>  net/dccp/ccids/ccid2.c |    9 +++++++++
>  net/ipv4/tcp_input.c   |    2 +-
>  3 files changed, 13 insertions(+), 10 deletions(-)
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 9179111..7118668 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -196,6 +196,9 @@ extern void tcp_time_wait(struct sock *sk, int state, int timeo);
>  /* TCP thin-stream limits */
>  #define TCP_THIN_LINEAR_RETRIES 6       /* After 6 linear retries, do exp. backoff */
>
> +/* TCP initial congestion window */
> +#define TCP_INIT_CWND          10
> +
>  extern struct inet_timewait_death_row tcp_death_row;
>
>  /* sysctl variables for tcp */
> @@ -799,15 +802,6 @@ static inline __u32 tcp_current_ssthresh(const struct sock *sk)
>  /* Use define here intentionally to get WARN_ON location shown at the caller */
>  #define tcp_verify_left_out(tp)        WARN_ON(tcp_left_out(tp) > tp->packets_out)
>
> -/*
> - * Convert RFC 3390 larger initial window into an equivalent number of packets.
> - * This is based on the numbers specified in RFC 5681, 3.1.
> - */
> -static inline u32 rfc3390_bytes_to_packets(const u32 smss)
> -{
> -       return smss <= 1095 ? 4 : (smss > 2190 ? 2 : 3);
> -}
> -
>  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);
>
> diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
> index e96d5e8..fadecd2 100644
> --- a/net/dccp/ccids/ccid2.c
> +++ b/net/dccp/ccids/ccid2.c
> @@ -583,6 +583,15 @@ done:
>        dccp_ackvec_parsed_cleanup(&hc->tx_av_chunks);
>  }
>
> +/*
> + * Convert RFC 3390 larger initial window into an equivalent number of packets.
> + * This is based on the numbers specified in RFC 5681, 3.1.
> + */
> +static inline u32 rfc3390_bytes_to_packets(const u32 smss)
> +{
> +       return smss <= 1095 ? 4 : (smss > 2190 ? 2 : 3);
> +}
> +
>  static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk)
>  {
>        struct ccid2_hc_tx_sock *hc = ccid_priv(ccid);
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index eb7f82e..2f692ce 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -817,7 +817,7 @@ __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
>        __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
>
>        if (!cwnd)
> -               cwnd = rfc3390_bytes_to_packets(tp->mss_cache);
> +               cwnd = TCP_INIT_CWND;
>        return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
>  }
>
> --
> 1.7.4
>
> --
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