From d6916f87ca5e566786f1a935a7cabba54774bbda Mon Sep 17 00:00:00 2001 From: Gerrit Renker Date: Sun, 24 Jul 2011 20:22:29 -0600 Subject: dccp: support for the exchange of NN options in established state 1/2 In contrast to static feature negotiation at the begin of a connection, this patch introduces support for exchange of dynamically changing options. Such an update/exchange is necessary in at least two cases: * CCID-2's Ack Ratio (RFC 4341, 6.1.2) which changes during the connection; * Sequence Window values that, as per RFC 4340, 7.5.2, should be sent "as the connection progresses". Both are non-negotiable (NN) features, which means that no new capabilities are negotiated, but rather that changes in known parameters are brought up-to-date at either end. Thse characteristics are reflected by the implementation: * only NN options can be exchanged after connection setup; * an ack is scheduled directly after activation to speed up the update; * CCIDs may request changes to an NN feature even if a negotiation for that feature is already underway: this is required by CCID-2, where changes in cwnd necessitate Ack Ratio changes, such that the previous Ack Ratio (which is still being negotiated) would cause irrecoverable RTO timeouts (thanks to work by Samuel Jero). Signed-off-by: Gerrit Renker Signed-off-by: Samuel Jero Acked-by: Ian McDonald --- net/dccp/dccp.h | 1 + net/dccp/feat.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ net/dccp/feat.h | 1 + 3 files changed, 67 insertions(+) (limited to 'net') diff --git a/net/dccp/dccp.h b/net/dccp/dccp.h index 5fdb07229017..583490aaf56f 100644 --- a/net/dccp/dccp.h +++ b/net/dccp/dccp.h @@ -474,6 +474,7 @@ static inline int dccp_ack_pending(const struct sock *sk) return dccp_ackvec_pending(sk) || inet_csk_ack_scheduled(sk); } +extern int dccp_feat_signal_nn_change(struct sock *sk, u8 feat, u64 nn_val); extern int dccp_feat_finalise_settings(struct dccp_sock *dp); extern int dccp_feat_server_ccid_dependencies(struct dccp_request_sock *dreq); extern int dccp_feat_insert_opts(struct dccp_sock*, struct dccp_request_sock*, diff --git a/net/dccp/feat.c b/net/dccp/feat.c index 568def952722..8bd28f244fef 100644 --- a/net/dccp/feat.c +++ b/net/dccp/feat.c @@ -12,6 +12,7 @@ * ----------- * o Feature negotiation is coordinated with connection setup (as in TCP), wild * changes of parameters of an established connection are not supported. + * o Changing non-negotiable (NN) values is supported in state OPEN/PARTOPEN. * o All currently known SP features have 1-byte quantities. If in the future * extensions of RFCs 4340..42 define features with item lengths larger than * one byte, a feature-specific extension of the code will be required. @@ -730,6 +731,70 @@ int dccp_feat_register_sp(struct sock *sk, u8 feat, u8 is_local, 0, list, len); } +/** + * dccp_feat_nn_get - Query current/pending value of NN feature + * @sk: DCCP socket of an established connection + * @feat: NN feature number from %dccp_feature_numbers + * For a known NN feature, returns value currently being negotiated, or + * current (confirmed) value if no negotiation is going on. + */ +u64 dccp_feat_nn_get(struct sock *sk, u8 feat) +{ + if (dccp_feat_type(feat) == FEAT_NN) { + struct dccp_sock *dp = dccp_sk(sk); + struct dccp_feat_entry *entry; + + entry = dccp_feat_list_lookup(&dp->dccps_featneg, feat, 1); + if (entry != NULL) + return entry->val.nn; + + switch (feat) { + case DCCPF_ACK_RATIO: + return dp->dccps_l_ack_ratio; + case DCCPF_SEQUENCE_WINDOW: + return dp->dccps_l_seq_win; + } + } + DCCP_BUG("attempt to look up unsupported feature %u", feat); + return 0; +} +EXPORT_SYMBOL_GPL(dccp_feat_nn_get); + +/** + * dccp_feat_signal_nn_change - Update NN values for an established connection + * @sk: DCCP socket of an established connection + * @feat: NN feature number from %dccp_feature_numbers + * @nn_val: the new value to use + * This function is used to communicate NN updates out-of-band. + */ +int dccp_feat_signal_nn_change(struct sock *sk, u8 feat, u64 nn_val) +{ + struct list_head *fn = &dccp_sk(sk)->dccps_featneg; + dccp_feat_val fval = { .nn = nn_val }; + struct dccp_feat_entry *entry; + + if (sk->sk_state != DCCP_OPEN && sk->sk_state != DCCP_PARTOPEN) + return 0; + + if (dccp_feat_type(feat) != FEAT_NN || + !dccp_feat_is_valid_nn_val(feat, nn_val)) + return -EINVAL; + + if (nn_val == dccp_feat_nn_get(sk, feat)) + return 0; /* already set or negotiation under way */ + + entry = dccp_feat_list_lookup(fn, feat, 1); + if (entry != NULL) { + dccp_pr_debug("Clobbering existing NN entry %llu -> %llu\n", + (unsigned long long)entry->val.nn, + (unsigned long long)nn_val); + dccp_feat_list_pop(entry); + } + + inet_csk_schedule_ack(sk); + return dccp_feat_push_change(fn, feat, 1, 0, &fval); +} +EXPORT_SYMBOL_GPL(dccp_feat_signal_nn_change); /* * Tracking features whose value depend on the choice of CCID diff --git a/net/dccp/feat.h b/net/dccp/feat.h index e56a4e5e634e..90b957d34d26 100644 --- a/net/dccp/feat.h +++ b/net/dccp/feat.h @@ -129,6 +129,7 @@ extern int dccp_feat_clone_list(struct list_head const *, struct list_head *); extern void dccp_encode_value_var(const u64 value, u8 *to, const u8 len); extern u64 dccp_decode_value_var(const u8 *bf, const u8 len); +extern u64 dccp_feat_nn_get(struct sock *sk, u8 feat); extern int dccp_insert_option_mandatory(struct sk_buff *skb); extern int dccp_insert_fn_opt(struct sk_buff *skb, u8 type, u8 feat, -- cgit v1.2.3 From 44e6fd9e67c1043aaeed381c10b74e73807b7f26 Mon Sep 17 00:00:00 2001 From: Gerrit Renker Date: Sun, 24 Jul 2011 20:27:59 -0600 Subject: dccp: support for exchanging of NN options in established state 2/2 This patch adds the receiver side and the (fast-path) activation part for dynamic changes of non-negotiable (NN) parameters in (PART)OPEN state. Signed-off-by: Gerrit Renker Signed-off-by: Samuel Jero Acked-by: Ian McDonald --- net/dccp/feat.c | 116 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 116 insertions(+) (limited to 'net') diff --git a/net/dccp/feat.c b/net/dccp/feat.c index 8bd28f244fef..ad6f9e2cac1a 100644 --- a/net/dccp/feat.c +++ b/net/dccp/feat.c @@ -344,6 +344,20 @@ static int __dccp_feat_activate(struct sock *sk, const int idx, return dccp_feat_table[idx].activation_hdlr(sk, val, rx); } +/** + * dccp_feat_activate - Activate feature value on socket + * @sk: fully connected DCCP socket (after handshake is complete) + * @feat_num: feature to activate, one of %dccp_feature_numbers + * @local: whether local (1) or remote (0) @feat_num is meant + * @fval: the value (SP or NN) to activate, or NULL to use the default value + * For general use this function is preferable over __dccp_feat_activate(). + */ +static int dccp_feat_activate(struct sock *sk, u8 feat_num, bool local, + dccp_feat_val const *fval) +{ + return __dccp_feat_activate(sk, dccp_feat_index(feat_num), local, fval); +} + /* Test for "Req'd" feature (RFC 4340, 6.4) */ static inline int dccp_feat_must_be_understood(u8 feat_num) { @@ -1251,6 +1265,100 @@ confirmation_failed: : DCCP_RESET_CODE_OPTION_ERROR; } +/** + * dccp_feat_handle_nn_established - Fast-path reception of NN options + * @sk: socket of an established DCCP connection + * @mandatory: whether @opt was preceded by a Mandatory option + * @opt: %DCCPO_CHANGE_L | %DCCPO_CONFIRM_R (NN only) + * @feat: NN number, one of %dccp_feature_numbers + * @val: NN value + * @len: length of @val in bytes + * This function combines the functionality of change_recv/confirm_recv, with + * the following differences (reset codes are the same): + * - cleanup after receiving the Confirm; + * - values are directly activated after successful parsing; + * - deliberately restricted to NN features. + * The restriction to NN features is essential since SP features can have non- + * predictable outcomes (depending on the remote configuration), and are inter- + * dependent (CCIDs for instance cause further dependencies). + */ +static u8 dccp_feat_handle_nn_established(struct sock *sk, u8 mandatory, u8 opt, + u8 feat, u8 *val, u8 len) +{ + struct list_head *fn = &dccp_sk(sk)->dccps_featneg; + const bool local = (opt == DCCPO_CONFIRM_R); + struct dccp_feat_entry *entry; + u8 type = dccp_feat_type(feat); + dccp_feat_val fval; + + dccp_feat_print_opt(opt, feat, val, len, mandatory); + + /* Ignore non-mandatory unknown and non-NN features */ + if (type == FEAT_UNKNOWN) { + if (local && !mandatory) + return 0; + goto fast_path_unknown; + } else if (type != FEAT_NN) { + return 0; + } + + /* + * We don't accept empty Confirms, since in fast-path feature + * negotiation the values are enabled immediately after sending + * the Change option. + * Empty Changes on the other hand are invalid (RFC 4340, 6.1). + */ + if (len == 0 || len > sizeof(fval.nn)) + goto fast_path_unknown; + + if (opt == DCCPO_CHANGE_L) { + fval.nn = dccp_decode_value_var(val, len); + if (!dccp_feat_is_valid_nn_val(feat, fval.nn)) + goto fast_path_unknown; + + if (dccp_feat_push_confirm(fn, feat, local, &fval) || + dccp_feat_activate(sk, feat, local, &fval)) + return DCCP_RESET_CODE_TOO_BUSY; + + /* set the `Ack Pending' flag to piggyback a Confirm */ + inet_csk_schedule_ack(sk); + + } else if (opt == DCCPO_CONFIRM_R) { + entry = dccp_feat_list_lookup(fn, feat, local); + if (entry == NULL || entry->state != FEAT_CHANGING) + return 0; + + fval.nn = dccp_decode_value_var(val, len); + /* + * Just ignore a value that doesn't match our current value. + * If the option changes twice within two RTTs, then at least + * one CONFIRM will be received for the old value after a + * new CHANGE was sent. + */ + if (fval.nn != entry->val.nn) + return 0; + + /* Only activate after receiving the Confirm option (6.6.1). */ + dccp_feat_activate(sk, feat, local, &fval); + + /* It has been confirmed - so remove the entry */ + dccp_feat_list_pop(entry); + + } else { + DCCP_WARN("Received illegal option %u\n", opt); + goto fast_path_failed; + } + return 0; + +fast_path_unknown: + if (!mandatory) + return dccp_push_empty_confirm(fn, feat, local); + +fast_path_failed: + return mandatory ? DCCP_RESET_CODE_MANDATORY_ERROR + : DCCP_RESET_CODE_OPTION_ERROR; +} + /** * dccp_feat_parse_options - Process Feature-Negotiation Options * @sk: for general use and used by the client during connection setup @@ -1286,6 +1394,14 @@ int dccp_feat_parse_options(struct sock *sk, struct dccp_request_sock *dreq, return dccp_feat_confirm_recv(fn, mandatory, opt, feat, val, len, server); } + break; + /* + * Support for exchanging NN options on an established connection. + */ + case DCCP_OPEN: + case DCCP_PARTOPEN: + return dccp_feat_handle_nn_established(sk, mandatory, opt, feat, + val, len); } return 0; /* ignore FN options in all other states */ } -- cgit v1.2.3 From a6444f4237af6c9981ddd45ab35a5c06d4e5a4d8 Mon Sep 17 00:00:00 2001 From: Samuel Jero Date: Sun, 24 Jul 2011 21:06:37 -0600 Subject: dccp: send Confirm options only once If a connection is in the OPEN state, remove feature negotiation Confirm options from the list of options after sending them once; as such options are NOT supposed to be retransmitted and are ONLY supposed to be sent in response to a Change option (RFC 4340 6.2). Signed-off-by: Samuel Jero Acked-by: Gerrit Renker --- net/dccp/feat.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-) (limited to 'net') diff --git a/net/dccp/feat.c b/net/dccp/feat.c index ad6f9e2cac1a..23cea0ee3101 100644 --- a/net/dccp/feat.c +++ b/net/dccp/feat.c @@ -665,11 +665,22 @@ int dccp_feat_insert_opts(struct dccp_sock *dp, struct dccp_request_sock *dreq, return -1; if (pos->needs_mandatory && dccp_insert_option_mandatory(skb)) return -1; - /* - * Enter CHANGING after transmitting the Change option (6.6.2). - */ - if (pos->state == FEAT_INITIALISING) - pos->state = FEAT_CHANGING; + + if (skb->sk->sk_state == DCCP_OPEN && + (opt == DCCPO_CONFIRM_R || opt == DCCPO_CONFIRM_L)) { + /* + * Confirms don't get retransmitted (6.6.3) once the + * connection is in state OPEN + */ + dccp_feat_list_pop(pos); + } else { + /* + * Enter CHANGING after transmitting the Change + * option (6.6.2). + */ + if (pos->state == FEAT_INITIALISING) + pos->state = FEAT_CHANGING; + } } return 0; } -- cgit v1.2.3 From 31daf0393fbb17cf6efe613fb538a3ea4b5202e4 Mon Sep 17 00:00:00 2001 From: Gerrit Renker Date: Sun, 24 Jul 2011 21:18:25 -0600 Subject: dccp ccid-2: use feature-negotiation to report Ack Ratio changes This uses the new feature-negotiation framework to signal Ack Ratio changes, as required by RFC 4341, sec. 6.1.2. That raises some problems with CCID-2, which at the moment can not cope gracefully with Ack Ratios > 1. Since these issues are not directly related to feature negotiation, they are marked by a FIXME. Signed-off-by: Gerrit Renker Signed-off-by: Samuel Jero Acked-by: Ian McDonald --- net/dccp/ccids/ccid2.c | 10 +++++++++- net/dccp/proto.c | 1 - 2 files changed, 9 insertions(+), 2 deletions(-) (limited to 'net') diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c index 0462040fc818..b51cc92376da 100644 --- a/net/dccp/ccids/ccid2.c +++ b/net/dccp/ccids/ccid2.c @@ -494,8 +494,16 @@ static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb) if (hc->tx_rpdupack >= NUMDUPACK) { hc->tx_rpdupack = -1; /* XXX lame */ hc->tx_rpseq = 0; - +#ifdef __CCID2_COPES_GRACEFULLY_WITH_ACK_CONGESTION_CONTROL__ + /* + * FIXME: Ack Congestion Control is broken; in + * the current state instabilities occurred with + * Ack Ratios greater than 1; causing hang-ups + * and long RTO timeouts. This needs to be fixed + * before opening up dynamic changes. -- gerrit + */ ccid2_change_l_ack_ratio(sk, 2 * dp->dccps_l_ack_ratio); +#endif } } } diff --git a/net/dccp/proto.c b/net/dccp/proto.c index 152975d942d9..e742f90a6858 100644 --- a/net/dccp/proto.c +++ b/net/dccp/proto.c @@ -184,7 +184,6 @@ int dccp_init_sock(struct sock *sk, const __u8 ctl_sock_initialized) dp->dccps_rate_last = jiffies; dp->dccps_role = DCCP_ROLE_UNDEFINED; dp->dccps_service = DCCP_SERVICE_CODE_IS_ABSENT; - dp->dccps_l_ack_ratio = dp->dccps_r_ack_ratio = 1; dp->dccps_tx_qlen = sysctl_dccp_tx_qlen; dccp_init_xmit_timers(sk); -- cgit v1.2.3 From d346d886a4c7f771c184e73833133f23a18de884 Mon Sep 17 00:00:00 2001 From: Samuel Jero Date: Sun, 24 Jul 2011 20:49:19 -0600 Subject: dccp ccid-2: prevent cwnd > Sequence Window Add a check to prevent CCID-2 from increasing the cwnd greater than the Sequence Window. When the congestion window becomes bigger than the Sequence Window, CCID-2 will attempt to keep more data in the network than the DCCP Sequence Window code considers possible. This results in the Sequence Window code issuing a Sync, thereby inducing needless overhead. Further, if this occurs at the sender, CCID-2 will never detect the problem because the Acks it receives will indicate no losses. I have seen this cause a drop of 1/3rd in throughput for a connection. Also add code to adjust the Sequence Window to be about 5 times the number of packets in the network (RFC 4340, 7.5.2) and to adjust the Ack Ratio so that the remote Sequence Window will hold about 5 times the number of packets in the network. This allows the congestion window to increase correctly without being limited by the Sequence Window. Signed-off-by: Samuel Jero Acked-by: Gerrit Renker --- net/dccp/ccids/ccid2.c | 50 +++++++++++++++++++++++++++++++++++--------------- net/dccp/ccids/ccid2.h | 6 ++++++ 2 files changed, 41 insertions(+), 15 deletions(-) (limited to 'net') diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c index b51cc92376da..9dbc4d88af16 100644 --- a/net/dccp/ccids/ccid2.c +++ b/net/dccp/ccids/ccid2.c @@ -85,7 +85,6 @@ static int ccid2_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb) static void ccid2_change_l_ack_ratio(struct sock *sk, u32 val) { - struct dccp_sock *dp = dccp_sk(sk); u32 max_ratio = DIV_ROUND_UP(ccid2_hc_tx_sk(sk)->tx_cwnd, 2); /* @@ -98,14 +97,15 @@ static void ccid2_change_l_ack_ratio(struct sock *sk, u32 val) DCCP_WARN("Limiting Ack Ratio (%u) to %u\n", val, max_ratio); val = max_ratio; } - if (val > DCCPF_ACK_RATIO_MAX) - val = DCCPF_ACK_RATIO_MAX; - - if (val == dp->dccps_l_ack_ratio) - return; + dccp_feat_signal_nn_change(sk, DCCPF_ACK_RATIO, + min_t(u32, val, DCCPF_ACK_RATIO_MAX)); +} - ccid2_pr_debug("changing local ack ratio to %u\n", val); - dp->dccps_l_ack_ratio = val; +static void ccid2_change_l_seq_window(struct sock *sk, u64 val) +{ + dccp_feat_signal_nn_change(sk, DCCPF_SEQUENCE_WINDOW, + clamp_val(val, DCCPF_SEQ_WMIN, + DCCPF_SEQ_WMAX)); } static void ccid2_hc_tx_rto_expire(unsigned long data) @@ -405,17 +405,37 @@ static void ccid2_new_ack(struct sock *sk, struct ccid2_seq *seqp, unsigned int *maxincr) { struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk); - - if (hc->tx_cwnd < hc->tx_ssthresh) { - if (*maxincr > 0 && ++hc->tx_packets_acked == 2) { + struct dccp_sock *dp = dccp_sk(sk); + int r_seq_used = hc->tx_cwnd / dp->dccps_l_ack_ratio; + + if (hc->tx_cwnd < dp->dccps_l_seq_win && + r_seq_used < dp->dccps_r_seq_win) { + if (hc->tx_cwnd < hc->tx_ssthresh) { + if (*maxincr > 0 && ++hc->tx_packets_acked == 2) { + hc->tx_cwnd += 1; + *maxincr -= 1; + hc->tx_packets_acked = 0; + } + } else if (++hc->tx_packets_acked >= hc->tx_cwnd) { hc->tx_cwnd += 1; - *maxincr -= 1; hc->tx_packets_acked = 0; } - } else if (++hc->tx_packets_acked >= hc->tx_cwnd) { - hc->tx_cwnd += 1; - hc->tx_packets_acked = 0; } + + /* + * Adjust the local sequence window and the ack ratio to allow about + * 5 times the number of packets in the network (RFC 4340 7.5.2) + */ + if (r_seq_used * CCID2_WIN_CHANGE_FACTOR >= dp->dccps_r_seq_win) + ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio * 2); + else if (r_seq_used * CCID2_WIN_CHANGE_FACTOR < dp->dccps_r_seq_win/2) + ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio / 2 ? : 1U); + + if (hc->tx_cwnd * CCID2_WIN_CHANGE_FACTOR >= dp->dccps_l_seq_win) + ccid2_change_l_seq_window(sk, dp->dccps_l_seq_win * 2); + else if (hc->tx_cwnd * CCID2_WIN_CHANGE_FACTOR < dp->dccps_l_seq_win/2) + ccid2_change_l_seq_window(sk, dp->dccps_l_seq_win / 2); + /* * FIXME: RTT is sampled several times per acknowledgment (for each * entry in the Ack Vector), instead of once per Ack (as in TCP SACK). diff --git a/net/dccp/ccids/ccid2.h b/net/dccp/ccids/ccid2.h index f585d330e1e5..18c97543e522 100644 --- a/net/dccp/ccids/ccid2.h +++ b/net/dccp/ccids/ccid2.h @@ -43,6 +43,12 @@ struct ccid2_seq { #define CCID2_SEQBUF_LEN 1024 #define CCID2_SEQBUF_MAX 128 +/* + * Multiple of congestion window to keep the sequence window at + * (RFC 4340 7.5.2) + */ +#define CCID2_WIN_CHANGE_FACTOR 5 + /** * struct ccid2_hc_tx_sock - CCID2 TX half connection * @tx_{cwnd,ssthresh,pipe}: as per RFC 4341, section 5 -- cgit v1.2.3 From 0ce95dc792549e0cf704e74aa8acb15a401f8cca Mon Sep 17 00:00:00 2001 From: Samuel Jero Date: Sun, 24 Jul 2011 21:05:16 -0600 Subject: dccp ccid-2: increment cwnd correctly This patch fixes an issue where CCID-2 will not increase the congestion window for numerous RTTs after an idle period, application-limited period, or a loss once the algorithm is in Congestion Avoidance. What happens is that, when CCID-2 is in Congestion Avoidance mode, it will increase hc->tx_packets_acked by one for every packet and will increment cwnd every cwnd packets. However, if there is now an idle period in the connection, cwnd will be reduced, possibly below the slow start threshold. This will cause the connection to go into Slow Start. However, in Slow Start CCID-2 performs this test to increment cwnd every second ack: ++hc->tx_packets_acked == 2 Unfortunately, this will be incorrect, if cwnd previous to the idle period was larger than 2 and if tx_packets_acked was close to cwnd. For example: cwnd=50 and tx_packets_acked=45. In this case, the current code, will increment tx_packets_acked until it equals two, which will only be once tx_packets_acked (an unsigned 32-bit integer) overflows. My fix is simply to change that test for tx_packets_acked greater than or equal to two in slow start. Signed-off-by: Samuel Jero Acked-by: Gerrit Renker --- net/dccp/ccids/ccid2.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'net') diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c index 9dbc4d88af16..d9dbd9ffe8cd 100644 --- a/net/dccp/ccids/ccid2.c +++ b/net/dccp/ccids/ccid2.c @@ -411,7 +411,7 @@ static void ccid2_new_ack(struct sock *sk, struct ccid2_seq *seqp, if (hc->tx_cwnd < dp->dccps_l_seq_win && r_seq_used < dp->dccps_r_seq_win) { if (hc->tx_cwnd < hc->tx_ssthresh) { - if (*maxincr > 0 && ++hc->tx_packets_acked == 2) { + if (*maxincr > 0 && ++hc->tx_packets_acked >= 2) { hc->tx_cwnd += 1; *maxincr -= 1; hc->tx_packets_acked = 0; -- cgit v1.2.3 From d96a9e8dd04cf5ab2782ca6192e395c5ca373f7d Mon Sep 17 00:00:00 2001 From: Samuel Jero Date: Sun, 24 Jul 2011 20:57:49 -0600 Subject: dccp ccid-2: check Ack Ratio when reducing cwnd This patch causes CCID-2 to check the Ack Ratio after reducing the congestion window. If the Ack Ratio is greater than the congestion window, it is reduced. This prevents timeouts caused by an Ack Ratio larger than the congestion window. In this situation, we choose to set the Ack Ratio to half the congestion window (or one if that's zero) so that if we loose one ack we don't trigger a timeout. Signed-off-by: Samuel Jero Acked-by: Gerrit Renker --- net/dccp/ccids/ccid2.c | 26 +++++++++++++++++++++++--- 1 file changed, 23 insertions(+), 3 deletions(-) (limited to 'net') diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c index d9dbd9ffe8cd..67164bb6ae4d 100644 --- a/net/dccp/ccids/ccid2.c +++ b/net/dccp/ccids/ccid2.c @@ -101,6 +101,24 @@ static void ccid2_change_l_ack_ratio(struct sock *sk, u32 val) min_t(u32, val, DCCPF_ACK_RATIO_MAX)); } +static void ccid2_check_l_ack_ratio(struct sock *sk) +{ + struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk); + + /* + * After a loss, idle period, application limited period, or RTO we + * need to check that the ack ratio is still less than the congestion + * window. Otherwise, we will send an entire congestion window of + * packets and got no response because we haven't sent ack ratio + * packets yet. + * If the ack ratio does need to be reduced, we reduce it to half of + * the congestion window (or 1 if that's zero) instead of to the + * congestion window. This prevents problems if one ack is lost. + */ + if (dccp_feat_nn_get(sk, DCCPF_ACK_RATIO) > hc->tx_cwnd) + ccid2_change_l_ack_ratio(sk, hc->tx_cwnd/2 ? : 1U); +} + static void ccid2_change_l_seq_window(struct sock *sk, u64 val) { dccp_feat_signal_nn_change(sk, DCCPF_SEQUENCE_WINDOW, @@ -187,6 +205,8 @@ static void ccid2_cwnd_application_limited(struct sock *sk, const u32 now) } hc->tx_cwnd_used = 0; hc->tx_cwnd_stamp = now; + + ccid2_check_l_ack_ratio(sk); } /* This borrows the code of tcp_cwnd_restart() */ @@ -205,6 +225,8 @@ static void ccid2_cwnd_restart(struct sock *sk, const u32 now) hc->tx_cwnd_stamp = now; hc->tx_cwnd_used = 0; + + ccid2_check_l_ack_ratio(sk); } static void ccid2_hc_tx_packet_sent(struct sock *sk, unsigned int len) @@ -461,9 +483,7 @@ static void ccid2_congestion_event(struct sock *sk, struct ccid2_seq *seqp) hc->tx_cwnd = hc->tx_cwnd / 2 ? : 1U; hc->tx_ssthresh = max(hc->tx_cwnd, 2U); - /* Avoid spurious timeouts resulting from Ack Ratio > cwnd */ - if (dccp_sk(sk)->dccps_l_ack_ratio > hc->tx_cwnd) - ccid2_change_l_ack_ratio(sk, hc->tx_cwnd); + ccid2_check_l_ack_ratio(sk); } static int ccid2_hc_tx_parse_options(struct sock *sk, u8 packet_type, -- cgit v1.2.3