Commit ff586298 authored by Gerrit Renker's avatar Gerrit Renker Committed by David S. Miller
Browse files

[DCCP] ccid3: Two optimisations for sending rate recomputation 



This performs two optimisations for the recomputation of the sending rate.

1) Currently the target sending rate X_calc is recalculated whenever
	a) the nofeedback timer expires, or
	b) a feedback packet is received.
   In the (a) case, recomputing X_calc is redundant, since

    * the parameters p and RTT do not change in between the
      reception of feedback packets;

    * the parameter X_recv is either modified from received
      feedback or via the nofeedback timer;

    * a test (`p == 0') in the nofeedback timer avoids using
      a stale/undefined value of X_calc if p was previously 0.

2) The nofeedback timer now only recomputes a timestamp when p == 0.
   This is according to step (4) of [RFC 3448, 4.3] and avoids
   unnecessarily determining a timestamp.

A debug statement about not updating X is also removed - it helps very
little in debugging and just clutters the logs.

Signed-off-by: default avatarGerrit Renker <gerrit@erg.abdn.ac.uk>
Acked-by: default avatarIan McDonald <ian.mcdonald@jandi.co.nz>
Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@mandriva.com>
parent 45393a66

net/dccp/ccids/ccid3.c

+16 −11
Original line number Diff line number Diff line
@@ -138,9 +138,6 @@ static void ccid3_hc_tx_update_x(struct sock *sk, struct timeval *now) 
	const __u32 old_x = hctx->ccid3hctx_x;



	if (hctx->ccid3hctx_p > 0) {

		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);
@@ -152,8 +149,7 @@ static void ccid3_hc_tx_update_x(struct sock *sk, struct timeval *now) 
					usecs_div(hctx->ccid3hctx_s,

					       	  hctx->ccid3hctx_rtt)   );

		hctx->ccid3hctx_t_ld = *now;

	} else

		ccid3_pr_debug("Not changing X\n");

	}



	if (hctx->ccid3hctx_x != old_x)

		ccid3_update_send_time(hctx);
@@ -223,9 +219,11 @@ static void ccid3_hc_tx_no_feedback_timer(unsigned long data) 
			ccid3_pr_debug("%s, sk=%p, state=%s, not idle\n",

				       dccp_role(sk), sk,

				       ccid3_tx_state_name(hctx->ccid3hctx_state));

			/* Halve sending rate */



			/*  If (p == 0 || X_calc > 2 * X_recv)

			/*

			 *  Modify the cached value of X_recv [RFC 3448, 4.4]

			 *

			 *  If (p == 0 || X_calc > 2 * X_recv)

			 *    X_recv = max(X_recv / 2, s / (2 * t_mbi));

			 *  Else

			 *    X_recv = X_calc / 4;
@@ -233,14 +231,15 @@ static void ccid3_hc_tx_no_feedback_timer(unsigned long data) 
			BUG_ON(hctx->ccid3hctx_p && !hctx->ccid3hctx_x_calc);



			if (hctx->ccid3hctx_p  == 0 ||

			    hctx->ccid3hctx_x_calc > 2 * hctx->ccid3hctx_x_recv)

			    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_T_MBI));

			else

				if (hctx->ccid3hctx_p == 0)

					dccp_timestamp(sk, &now);

			} else

				hctx->ccid3hctx_x_recv = hctx->ccid3hctx_x_calc / 4;



			/* Update sending rate */

			dccp_timestamp(sk, &now);

			/* Now recalculate X [RFC 3448, 4.3, step (4)] */

			ccid3_hc_tx_update_x(sk, &now);

		}

		/*
@@ -496,6 +495,12 @@ static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) 
			hctx->ccid3hctx_rtt = (9 * hctx->ccid3hctx_rtt +

					           (u32)r_sample        ) / 10;



			/* Update sending rate (step 4 of [RFC 3448, 4.3]) */

			if (hctx->ccid3hctx_p > 0)

				hctx->ccid3hctx_x_calc =

					tfrc_calc_x(hctx->ccid3hctx_s,

						    hctx->ccid3hctx_rtt,

						    hctx->ccid3hctx_p);

			ccid3_hc_tx_update_x(sk, &now);



			ccid3_pr_debug("%s(%p), RTT=%uus (sample=%ldus), s=%u, "

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