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Commit 792e6d33 authored by Gerrit Renker's avatar Gerrit Renker
Browse files

dccp tfrc/ccid-3: computing the loss rate from the Loss Event Rate 



This adds a function to take care of the following, separate cases occurring in
the computation of the Loss Rate p:

 * 1/(2^32-1) is mapped into 0% as per RFC 4342, 8.5;
 * 1/0        is mapped into 100%, the maximum;
 * to avoid that p = 1/x is rounded down to 0 when x is very large, since this
   means accidentally re-entering slow-start indicated by p == 0, the minimum
   resolution value of p is now returned instead;
 * a bug in ccid3_hc_rx_getsockopt is fixed: 1/0 was mapped into ~0U.

Signed-off-by: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
parent 80763dfb

net/dccp/ccids/ccid3.c

+4 −5
Original line number Diff line number Diff line
@@ -400,10 +400,10 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) 


	/* Update loss event rate (which is scaled by 1e6) */

	pinv = opt_recv->ccid3or_loss_event_rate;

	if (pinv == ~0U || pinv == 0)	       /* see RFC 4342, 8.5   */

	if (pinv == 0)

		hc->tx_p = 0;

	else				       /* can not exceed 100% */

		hc->tx_p = scaled_div(1, pinv);

	else

		hc->tx_p = tfrc_invert_loss_event_rate(pinv);



	/*

	 * Update allowed sending rate X as per draft rfc3448bis-00, 4.2/3
@@ -834,8 +834,7 @@ static int ccid3_hc_rx_getsockopt(struct sock *sk, const int optname, int len, 
			return -EINVAL;

		rx_info.tfrcrx_x_recv = hc->rx_x_recv;

		rx_info.tfrcrx_rtt    = hc->rx_rtt;

		rx_info.tfrcrx_p      = hc->rx_pinv == 0 ? ~0U :

					   scaled_div(1, hc->rx_pinv);

		rx_info.tfrcrx_p      = tfrc_invert_loss_event_rate(hc->rx_pinv);

		len = sizeof(rx_info);

		val = &rx_info;

		break;

net/dccp/ccids/lib/tfrc.h

+1 −0
Original line number Diff line number Diff line
@@ -57,6 +57,7 @@ static inline u32 tfrc_ewma(const u32 avg, const u32 newval, const u8 weight) 


extern u32  tfrc_calc_x(u16 s, u32 R, u32 p);

extern u32  tfrc_calc_x_reverse_lookup(u32 fvalue);

extern u32  tfrc_invert_loss_event_rate(u32 loss_event_rate);



extern int  tfrc_tx_packet_history_init(void);

extern void tfrc_tx_packet_history_exit(void);

net/dccp/ccids/lib/tfrc_equation.c

+14 −0
Original line number Diff line number Diff line
@@ -687,3 +687,17 @@ u32 tfrc_calc_x_reverse_lookup(u32 fvalue) 
	index = tfrc_binsearch(fvalue, 0);

	return (index + 1) * 1000000 / TFRC_CALC_X_ARRSIZE;

}



/**

 * tfrc_invert_loss_event_rate  -  Compute p so that 10^6 corresponds to 100%

 * When @loss_event_rate is large, there is a chance that p is truncated to 0.

 * To avoid re-entering slow-start in that case, we set p = TFRC_SMALLEST_P > 0.

 */

u32 tfrc_invert_loss_event_rate(u32 loss_event_rate)

{

	if (loss_event_rate == UINT_MAX)		/* see RFC 4342, 8.5 */

		return 0;

	if (unlikely(loss_event_rate == 0))		/* map 1/0 into 100% */

		return 1000000;

	return max_t(u32, scaled_div(1, loss_event_rate), TFRC_SMALLEST_P);

}