Quoting Eddie Kohler:
| Gerrit, everyone,
|
| Again, the INTENTION I think was for the 2-4 packets per RTT to apply
| IMMEDIATELY, because the Request-Response exchange gave you an initial RTT
| estimate. But this is just not what RFC 4342 says. When I figure this out
| with Sally we will get back to you, and perhaps publish an erratum, allowing
| Linux to have the correct behavior while remaining 'standards compliant'.
see previous reply
|
| Eddie
|
|
| Gerrit Renker wrote:
| > [CCID 3]: Larger initial windows
| >
| > This implements the larger-initial-windows feature for CCID 3, as described
| > in section 5 of RFC 4342. When the first feedback packet arrives, the sender
| > can send up to 2..4 packets per RTT, instead of just one.
| >
| > The patch further
| > * reduces the number of timestamping calls by passing the timestamp value
| > (which is computed in one of the calling functions anyway) as argument
| >
| > * renames one constant with a very long name into one which is shorter and
| > resembles the one in RFC 3448 (t_mbi)
| >
| > * simplifies some of the min_t/max_t cases where both `x', `y' have the same
| > type
| >
| > Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx>
| > ---
| > net/dccp/ccids/ccid3.c | 75 +++++++++++++++++++++++++++----------------------
| > net/dccp/ccids/ccid3.h | 4 +-
| > 2 files changed, 44 insertions(+), 35 deletions(-)
| >
| > --- a/net/dccp/ccids/ccid3.c
| > +++ b/net/dccp/ccids/ccid3.c
| > @@ -129,35 +129,42 @@ static inline void ccid3_update_send_tim
| > * If X has changed, we also update the scheduled send time t_now,
| > * the inter-packet interval t_ipi, and the delta value.
| > */
| > -static void ccid3_hc_tx_update_x(struct sock *sk)
| > +static void ccid3_hc_tx_update_x(struct sock *sk, struct timeval *now)
| > +
| > {
| > struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
| > const __u32 old_x = hctx->ccid3hctx_x;
| >
| > DCCP_BUG_ON(hctx->ccid3hctx_rtt == 0);
| >
| > - /* To avoid large error in calcX */
| > - if (hctx->ccid3hctx_p >= TFRC_SMALLEST_P) {
| > - hctx->ccid3hctx_x_calc = tfrc_calc_x(hctx->ccid3hctx_s,
| > - hctx->ccid3hctx_rtt,
| > - hctx->ccid3hctx_p);
| > - hctx->ccid3hctx_x = max_t(u32, min_t(u32, hctx->ccid3hctx_x_calc,
| > - 2 * hctx->ccid3hctx_x_recv),
| > - (hctx->ccid3hctx_s /
| > - TFRC_MAX_BACK_OFF_TIME));
| > - } else {
| > - struct timeval now;
| > + /* Compute X after the first feedback packet has arrived */
| > + if (hctx->ccid3hctx_state == TFRC_SSTATE_NO_FBACK) {
| > + /* This implements `Larger Initial Windows' [RFC 4342, sec. 5]
| > + * We deviate in that we use `s' instead of `MSS'. */
| > + u16 w_init = max( 4 * hctx->ccid3hctx_s,
| > + max( 2 * hctx->ccid3hctx_s, 4380));
| > + hctx->ccid3hctx_x = usecs_div(w_init, hctx->ccid3hctx_rtt);
| > + hctx->ccid3hctx_t_ld = *now;
| > +
| > + /* To avoid large error in calcX */
| > + } else if (hctx->ccid3hctx_p >= TFRC_SMALLEST_P) {
| > + hctx->ccid3hctx_x_calc = tfrc_calc_x(hctx->ccid3hctx_s,
| > + hctx->ccid3hctx_rtt,
| > + hctx->ccid3hctx_p);
| > + hctx->ccid3hctx_x = max_t(u32, min(hctx->ccid3hctx_x_calc,
| > + hctx->ccid3hctx_x_recv * 2),
| > + hctx->ccid3hctx_s / TFRC_t_mbi );
| > +
| > + } else if (timeval_delta(now, &hctx->ccid3hctx_t_ld) >=
| > + hctx->ccid3hctx_rtt) {
| > + hctx->ccid3hctx_x = max(min(hctx->ccid3hctx_x_recv,
| > + hctx->ccid3hctx_x ) * 2,
| > + usecs_div(hctx->ccid3hctx_s,
| > + hctx->ccid3hctx_rtt) );
| > + hctx->ccid3hctx_t_ld = *now;
| > + } else
| > + ccid3_pr_debug("Not changing X\n");
| >
| > - dccp_timestamp(sk, &now);
| > - if (timeval_delta(&now, &hctx->ccid3hctx_t_ld) >=
| > - hctx->ccid3hctx_rtt) {
| > - hctx->ccid3hctx_x = max_t(u32, min_t(u32, hctx->ccid3hctx_x_recv,
| > - hctx->ccid3hctx_x) * 2,
| > - usecs_div(hctx->ccid3hctx_s,
| > - hctx->ccid3hctx_rtt));
| > - hctx->ccid3hctx_t_ld = now;
| > - }
| > - }
| > if(hctx->ccid3hctx_x != old_x)
| > ccid3_update_send_time(hctx);
| > }
| > @@ -185,6 +192,7 @@ static void ccid3_hc_tx_no_feedback_time
| > struct sock *sk = (struct sock *)data;
| > struct ccid3_hc_tx_sock *hctx = ccid3_hc_tx_sk(sk);
| > unsigned long next_tmout = USEC_PER_SEC / 5;
| > + struct timeval now;
| >
| > bh_lock_sock(sk);
| > if (sock_owned_by_user(sk)) {
| > @@ -200,10 +208,8 @@ static void ccid3_hc_tx_no_feedback_time
| > case TFRC_SSTATE_NO_FBACK:
| > /* Halve send rate */
| > hctx->ccid3hctx_x /= 2;
| > - if (hctx->ccid3hctx_x < (hctx->ccid3hctx_s /
| > - TFRC_MAX_BACK_OFF_TIME))
| > - hctx->ccid3hctx_x = (hctx->ccid3hctx_s /
| > - TFRC_MAX_BACK_OFF_TIME);
| > + if (hctx->ccid3hctx_x < (hctx->ccid3hctx_s / TFRC_t_mbi))
| > + hctx->ccid3hctx_x = hctx->ccid3hctx_s / TFRC_t_mbi;
| >
| > ccid3_pr_debug("%s, sk=%p, state=%s, updated tx rate to %d "
| > "bytes/s\n",
| > @@ -240,12 +246,13 @@ static void ccid3_hc_tx_no_feedback_time
| > if (hctx->ccid3hctx_p < TFRC_SMALLEST_P ||
| > hctx->ccid3hctx_x_calc > 2 * hctx->ccid3hctx_x_recv)
| > hctx->ccid3hctx_x_recv = max_t(u32, hctx->ccid3hctx_x_recv / 2,
| > - hctx->ccid3hctx_s / (2 * TFRC_MAX_BACK_OFF_TIME));
| > + hctx->ccid3hctx_s / (2 * TFRC_t_mbi));
| > else
| > hctx->ccid3hctx_x_recv = hctx->ccid3hctx_x_calc / 4;
| >
| > /* Update sending rate */
| > - ccid3_hc_tx_update_x(sk);
| > + dccp_timestamp(sk, &now);
| > + ccid3_hc_tx_update_x(sk, &now);
| > }
| > /*
| > * Schedule no feedback timer to expire in
| > @@ -488,10 +495,9 @@ static void ccid3_hc_tx_packet_recv(stru
| > *
| > * q is a constant, RFC 3448 recomments 0.9
| > */
| > - if (hctx->ccid3hctx_state == TFRC_SSTATE_NO_FBACK) {
| > - ccid3_hc_tx_set_state(sk, TFRC_SSTATE_FBACK);
| > + if (hctx->ccid3hctx_state == TFRC_SSTATE_NO_FBACK)
| > hctx->ccid3hctx_rtt = r_sample;
| > - } else
| > + else
| > hctx->ccid3hctx_rtt = (hctx->ccid3hctx_rtt * 9) / 10 +
| > r_sample / 10;
| >
| > @@ -508,7 +514,11 @@ static void ccid3_hc_tx_packet_recv(stru
| > sk_stop_timer(sk, &hctx->ccid3hctx_no_feedback_timer);
| >
| > /* Update sending rate (and likely t_ipi, t_nom, and delta) */
| > - ccid3_hc_tx_update_x(sk);
| > + ccid3_hc_tx_update_x(sk, &now);
| > +
| > + /* Update the state if necessary */
| > + if (hctx->ccid3hctx_state == TFRC_SSTATE_NO_FBACK)
| > + ccid3_hc_tx_set_state(sk, TFRC_SSTATE_FBACK);
| >
| > /* remove all packets older than the one acked from history */
| > dccp_tx_hist_purge_older(ccid3_tx_hist,
| > @@ -519,7 +529,6 @@ static void ccid3_hc_tx_packet_recv(stru
| > */
| > sk->sk_write_space(sk);
| >
| > -
| > /* Update timeout interval. We use the alternative variant of
| > * [RFC 3448, 3.1] which sets the upper bound of t_rto to one
| > * second, as it is suggested for TCP (see RFC 2988, 2.4). */
| > --- a/net/dccp/ccids/ccid3.h
| > +++ b/net/dccp/ccids/ccid3.h
| > @@ -48,8 +48,8 @@
| > /* In usecs - half the scheduling granularity as per RFC3448 4.6 */
| > #define TFRC_OPSYS_HALF_TIME_GRAN (USEC_PER_SEC / (2 * HZ))
| >
| > -/* In seconds */
| > -#define TFRC_MAX_BACK_OFF_TIME 64
| > +/* Parameter t_mbi from [RFC 3448, 4.3]: In seconds */
| > +#define TFRC_t_mbi 64
| >
| > #define TFRC_SMALLEST_P 40
| >
| > -
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