On Mon, 30 Aug 2010, Gerrit Renker wrote:
> This patch consolidates initial-window code common to TCP and CCID-2:
> * TCP uses RFC 3390 in a packet-oriented manner (tcp_input.c) and
> * CCID-2 uses RFC 3390 in packet-oriented manner (RFC 4341).
>
> Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx>
> ---
> include/net/tcp.h | 15 +++++++++++++++
> net/dccp/ccids/ccid2.c | 8 ++------
> net/ipv4/tcp_input.c | 17 ++---------------
> 3 files changed, 19 insertions(+), 21 deletions(-)
>
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -789,6 +789,21 @@ 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.
> + *
> + * John Heffner states:
> + *
> + * The RFC specifies a window of no more than 4380 bytes
> + * unless 2*MSS > 4380. Reading the pseudocode in the RFC
> + * is a bit misleading because they use a clamp at 4380 bytes
> + * rather than a multiplier in the relevant range.
> + */
> +static inline u32 rfc3390_bytes_to_packets(const u32 smss)
> +{
> + return smss <= 1095 ? 4 : (smss > 1460 ? 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);
>
> --- a/net/dccp/ccids/ccid2.c
> +++ b/net/dccp/ccids/ccid2.c
> @@ -641,12 +641,8 @@ static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk)
> /* RFC 4341, 5: initialise ssthresh to arbitrarily high (max) value */
> hc->tx_ssthresh = ~0U;
>
> - /*
> - * RFC 4341, 5: "The cwnd parameter is initialized to at most four
> - * packets for new connections, following the rules from [RFC3390]".
> - * We need to convert the bytes of RFC3390 into the packets of RFC 4341.
> - */
> - hc->tx_cwnd = clamp(4380U / dp->dccps_mss_cache, 2U, 4U);
> + /* Use larger initial windows (RFC 4341, section 5). */
> + hc->tx_cwnd = rfc3390_bytes_to_packets(dp->dccps_mss_cache);
>
> /* Make sure that Ack Ratio is enabled and within bounds. */
> max_ratio = DIV_ROUND_UP(hc->tx_cwnd, 2);
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -805,25 +805,12 @@ void tcp_update_metrics(struct sock *sk)
> }
> }
>
> -/* Numbers are taken from RFC3390.
> - *
> - * John Heffner states:
> - *
> - * The RFC specifies a window of no more than 4380 bytes
> - * unless 2*MSS > 4380. Reading the pseudocode in the RFC
> - * is a bit misleading because they use a clamp at 4380 bytes
> - * rather than use a multiplier in the relevant range.
> - */
> __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst)
> {
> __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
>
> - if (!cwnd) {
> - if (tp->mss_cache > 1460)
> - cwnd = 2;
> - else
> - cwnd = (tp->mss_cache > 1095) ? 3 : 4;
> - }
> + if (!cwnd)
> + cwnd = rfc3390_bytes_to_packets(tp->mss_cache);
> return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
> }
What is spelled out in tcp_select_initial_window might also need to follow
the same logic?
--
i.
--
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