Commit 535c55df authored by Gerrit Renker's avatar Gerrit Renker
Browse files

dccp tfrc/ccid-3: Computing Loss Rate from Loss Event Rate 



This adds a function to take care of the following 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 the maximum of 100%;
 * we want 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).

In the last case, the minimum-resolution value of p is returned.

Furthermore, a bug in ccid3_hc_rx_getsockopt is fixed (1/0 was mapped into ~0U),
which now allows to consistently print the scaled p-values as

        printf("Loss Event Rate = %u.%04u %%\n", rx_info.tfrcrx_p / 10000, 
                                                 rx_info.tfrcrx_p % 10000);

Signed-off-by: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
parent 3306c781

net/dccp/ccids/ccid3.c

+4 −5
Original line number Diff line number Diff line
@@ -410,10 +410,10 @@ 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)

		hctx->p = 0;

	else				       /* can not exceed 100% */

		hctx->p = scaled_div(1, pinv);

	else

		hctx->p = tfrc_invert_loss_event_rate(pinv);



	/*

	 * Update allowed sending rate X as per draft rfc3448bis-00, 4.2/3
@@ -854,8 +854,7 @@ static int ccid3_hc_rx_getsockopt(struct sock *sk, const int optname, int len, 
			return -EINVAL;

		rx_info.tfrcrx_x_recv = hcrx->x_recv;

		rx_info.tfrcrx_rtt    = hcrx->rtt;

		rx_info.tfrcrx_p      = hcrx->p_inverse == 0 ? ~0U :

					   scaled_div(1, hcrx->p_inverse);

		rx_info.tfrcrx_p      = tfrc_invert_loss_event_rate(hcrx->p_inverse);

		len = sizeof(rx_info);

		val = &rx_info;

		break;

net/dccp/ccids/lib/tfrc.h

+1 −0
Original line number Diff line number Diff line
@@ -58,6 +58,7 @@ 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

+15 −2
Original line number Diff line number Diff line
@@ -658,7 +658,6 @@ u32 tfrc_calc_x(u16 s, u32 R, u32 p) 
	result = scaled_div(s, R);

	return scaled_div32(result, f);

}



EXPORT_SYMBOL_GPL(tfrc_calc_x);



/**
@@ -693,5 +692,19 @@ u32 tfrc_calc_x_reverse_lookup(u32 fvalue) 
	index = tfrc_binsearch(fvalue, 0);

	return (index + 1) * 1000000 / TFRC_CALC_X_ARRSIZE;

}



EXPORT_SYMBOL_GPL(tfrc_calc_x_reverse_lookup);



/**

 * 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);

}

EXPORT_SYMBOL_GPL(tfrc_invert_loss_event_rate);

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