Commit 374bcf32 authored by Andrea Bittau's avatar Andrea Bittau Committed by David S. Miller
Browse files

[DCCP] CCID2: Halve cwnd once upon multiple losses in a single RTT 



When multiple losses occur in one RTT, the window should be halved
only once [a single "congestion event"].  This is now implemented,
although not perfectly.  Slightly changed the interface for changing
the cwnd: pass hctx instead of dp.  This is required in order to allow
for change_cwnd to be called from _init().

Signed-off-by: default avatarAndrea Bittau <a.bittau@cs.ucl.ac.uk>
Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 07978aab

net/dccp/ccids/ccid2.c

+31 −18
Original line number Diff line number Diff line
@@ -187,10 +187,8 @@ static void ccid2_change_l_ack_ratio(struct sock *sk, int val) 
	dp->dccps_l_ack_ratio = val;

}



static void ccid2_change_cwnd(struct sock *sk, int val)

static void ccid2_change_cwnd(struct ccid2_hc_tx_sock *hctx, int val)

{

	struct ccid2_hc_tx_sock *hctx = ccid2_hc_tx_sk(sk);



	if (val == 0)

		val = 1;
@@ -234,7 +232,7 @@ static void ccid2_hc_tx_rto_expire(unsigned long data) 
	hctx->ccid2hctx_ssthresh = hctx->ccid2hctx_cwnd >> 1;

	if (hctx->ccid2hctx_ssthresh < 2)

		hctx->ccid2hctx_ssthresh = 2;

	ccid2_change_cwnd(sk, 1);

	ccid2_change_cwnd(hctx, 1);



	/* clear state about stuff we sent */

	hctx->ccid2hctx_seqt	= hctx->ccid2hctx_seqh;
@@ -444,7 +442,7 @@ static inline void ccid2_new_ack(struct sock *sk, 
			/* increase every 2 acks */

			hctx->ccid2hctx_ssacks++;

			if (hctx->ccid2hctx_ssacks == 2) {

				ccid2_change_cwnd(sk, hctx->ccid2hctx_cwnd + 1);

				ccid2_change_cwnd(hctx, hctx->ccid2hctx_cwnd+1);

				hctx->ccid2hctx_ssacks = 0;

				*maxincr = *maxincr - 1;

			}
@@ -457,7 +455,7 @@ static inline void ccid2_new_ack(struct sock *sk, 
		hctx->ccid2hctx_acks++;



		if (hctx->ccid2hctx_acks >= hctx->ccid2hctx_cwnd) {

			ccid2_change_cwnd(sk, hctx->ccid2hctx_cwnd + 1);

			ccid2_change_cwnd(hctx, hctx->ccid2hctx_cwnd + 1);

			hctx->ccid2hctx_acks = 0;

		}

	}
@@ -532,6 +530,22 @@ static void ccid2_hc_tx_dec_pipe(struct sock *sk) 
		ccid2_hc_tx_kill_rto_timer(sk);

}



static void ccid2_congestion_event(struct ccid2_hc_tx_sock *hctx,

				   struct ccid2_seq *seqp)

{

	if (time_before(seqp->ccid2s_sent, hctx->ccid2hctx_last_cong)) {

		ccid2_pr_debug("Multiple losses in an RTT---treating as one\n");

		return;

	}



	hctx->ccid2hctx_last_cong = jiffies;



	ccid2_change_cwnd(hctx, hctx->ccid2hctx_cwnd >> 1);

	hctx->ccid2hctx_ssthresh = hctx->ccid2hctx_cwnd;

	if (hctx->ccid2hctx_ssthresh < 2)

		hctx->ccid2hctx_ssthresh = 2;

}



static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)

{

	struct dccp_sock *dp = dccp_sk(sk);
@@ -542,7 +556,6 @@ static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) 
	unsigned char veclen;

	int offset = 0;

	int done = 0;

	int loss = 0;

	unsigned int maxincr = 0;



	ccid2_hc_tx_check_sanity(hctx);
@@ -636,7 +649,8 @@ static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) 
				    !seqp->ccid2s_acked) {

				    	if (state ==

					    DCCP_ACKVEC_STATE_ECN_MARKED) {

						loss = 1;

					    	ccid2_congestion_event(hctx,

								       seqp);

					} else

						ccid2_new_ack(sk, seqp,

							      &maxincr);
@@ -688,7 +702,13 @@ static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) 
		/* check for lost packets */

		while (1) {

			if (!seqp->ccid2s_acked) {

				loss = 1;

				ccid2_pr_debug("Packet lost: %llu\n",

					       seqp->ccid2s_seq);

				/* XXX need to traverse from tail -> head in

				 * order to detect multiple congestion events in

				 * one ack vector.

				 */

				ccid2_congestion_event(hctx, seqp);

				ccid2_hc_tx_dec_pipe(sk);

			}

			if (seqp == hctx->ccid2hctx_seqt)
@@ -707,14 +727,6 @@ static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) 
		hctx->ccid2hctx_seqt = hctx->ccid2hctx_seqt->ccid2s_next;

	}



	if (loss) {

		/* XXX do bit shifts guarantee a 0 as the new bit? */

		ccid2_change_cwnd(sk, hctx->ccid2hctx_cwnd >> 1);

		hctx->ccid2hctx_ssthresh = hctx->ccid2hctx_cwnd;

		if (hctx->ccid2hctx_ssthresh < 2)

			hctx->ccid2hctx_ssthresh = 2;

	}



	ccid2_hc_tx_check_sanity(hctx);

}
@@ -722,7 +734,7 @@ static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk) 
{

        struct ccid2_hc_tx_sock *hctx = ccid_priv(ccid);



	hctx->ccid2hctx_cwnd	  = 1;

	ccid2_change_cwnd(hctx, 1);

	/* Initialize ssthresh to infinity.  This means that we will exit the

	 * initial slow-start after the first packet loss.  This is what we

	 * want.
@@ -741,6 +753,7 @@ static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk) 
	hctx->ccid2hctx_rttvar	 = -1;

	hctx->ccid2hctx_lastrtt  = 0;

	hctx->ccid2hctx_rpdupack = -1;

	hctx->ccid2hctx_last_cong = jiffies;



	hctx->ccid2hctx_rtotimer.function = &ccid2_hc_tx_rto_expire;

	hctx->ccid2hctx_rtotimer.data	  = (unsigned long)sk;

net/dccp/ccids/ccid2.h

+1 −0
Original line number Diff line number Diff line
@@ -71,6 +71,7 @@ struct ccid2_hc_tx_sock { 
	u64			ccid2hctx_rpseq;

	int			ccid2hctx_rpdupack;

	int			ccid2hctx_sendwait;

	unsigned long		ccid2hctx_last_cong;

};



struct ccid2_hc_rx_sock {