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* [TCP]: DSACK signals data receival, be conservativeIlpo Järvinen2007-08-02
| | | | | | | | In case a DSACK is received, it's better to lower cwnd as it's a sign of data receival. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Also handle snd_una changes in tcp_cwnd_downIlpo Järvinen2007-08-02
| | | | | | | | | | | | | | | | | | | | | | tcp_cwnd_down must check for it too as it should be conservative in case of collapse stuff and also when receiver is trying to lie (though that wouldn't be very successful/useful anyway). Note: - Separated also is_dupack and do_lost in fast_retransalert * Much cleaner look-and-feel now * This time it really fixes cumulative ACK with many new SACK blocks recovery entry (I claimed this fixes with last patch but it wasn't). TCP will now call tcp_update_scoreboard regardless of is_dupack when in recovery as long as there is enough fackets_out. - Introduce FLAG_SND_UNA_ADVANCED * Some prior_snd_una arguments are unnecessary after it - Added helper FLAG_ANY_PROGRESS to avoid long FLAG...|FLAG... constructs Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Bidir flow must not disregard SACK blocks for lost markingIlpo Järvinen2007-07-31
| | | | | | | | | | | | | | | | | | | It's possible that new SACK blocks that should trigger new LOST markings arrive with new data (which previously made is_dupack false). In addition, I think this fixes a case where we get a cumulative ACK with enough SACK blocks to trigger the fast recovery (is_dupack would be false there too). I'm not completely pleased with this solution because readability of the code is somewhat questionable as 'is_dupack' in SACK case is no longer about dupacks only but would mean something like 'lost_marker_work_todo' too... But because of Eifel stuff done in CA_Recovery, the FLAG_DATA_SACKED check cannot be placed to the if statement which seems attractive solution. Nevertheless, I didn't like adding another variable just for that either... :-) Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Fix ratehalving with bidirectional flowsIlpo Järvinen2007-07-31
| | | | | | | | | | | | | Actually, the ratehalving seems to work too well, as cwnd is reduced on every second ACK even though the packets in flight remains unchanged. Recoveries in a bidirectional flows suffer quite badly because of this, both NewReno and SACK are affected. After this patch, rate halving is performed for ACK only if packets in flight was supposedly changed too. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: congestion control API pass RTT in microsecondsStephen Hemminger2007-07-31
| | | | | | | | | | | | | | | | | This patch changes the API for the callback that is done after an ACK is received. It solves a couple of issues: * Some congestion controls want higher resolution value of RTT (controlled by TCP_CONG_RTT_SAMPLE flag). These don't really want a ktime, but all compute a RTT in microseconds. * Other congestion control could use RTT at jiffies resolution. To keep API consistent the units should be the same for both cases, just the resolution should change. Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: remove unused argument to cong_avoid opStephen Hemminger2007-07-18
| | | | | | | | | None of the existing TCP congestion controls use the rtt value pased in the ca_ops->cong_avoid interface. Which is lucky because seq_rtt could have been -1 when handling a duplicate ack. Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Verify the presence of RETRANS bit when leaving FRTOIlpo Järvinen2007-07-15
| | | | | | | | For yet unknown reason, something cleared SACKED_RETRANS bit underneath FRTO. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Fix logic breakage due to DSACK separationIlpo Järvinen2007-06-15
| | | | | | | | | | Commit 6f74651ae626ec672028587bc700538076dfbefb is found guilty of breaking DSACK counting, which should be done only for the SACK block reported by the DSACK instead of every SACK block that is received along with DSACK information. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Congestion control API RTT sampling fixIlpo Järvinen2007-06-15
| | | | | | | | | | | | | | Commit 164891aadf1721fca4dce473bb0e0998181537c6 broke RTT sampling of congestion control modules. Inaccurate timestamps could be fed to them without providing any way for them to identify such cases. Previously RTT sampler was called only if FLAG_RETRANS_DATA_ACKED was not set filtering inaccurate timestamps nicely. In addition, the new behavior could give an invalid timestamp (zero) to RTT sampler if only skbs with TCPCB_RETRANS were ACKed. This solves both problems. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Add missing break to TCP option parsing codeIlpo Järvinen2007-06-14
| | | | | | | This flaw does not affect any behavior (currently). Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Fix left_out setting during FRTOIlpo Järvinen2007-06-12
| | | | | | | | | | | Without FRTO, the tcp_try_to_open is never called with lost_out > 0 (see tcp_time_to_recover). However, when FRTO is enabled, the !tp->lost condition is not used until end of FRTO because that way TCP avoids premature entry to fast recovery during FRTO. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Fix GSO ignorance of pkts_acked arg (cong.cntrl modules)Ilpo Järvinen2007-06-03
| | | | | | | | | | | | The code used to ignore GSO completely, passing either way too small or zero pkts_acked when GSO skb or part of it got ACKed. In addition, there is no need to calculate the value in the loop but simple arithmetics after the loop is sufficient. There is no need to handle SYN case specially because congestion control modules are not yet initialized when FLAG_SYN_ACKED is set. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP] FRTO: Prevent state inconsistency in corner casesIlpo Järvinen2007-05-19
| | | | | | | | | | | | | | | | State could become inconsistent in two cases: 1) Userspace disabled FRTO by tuning sysctl when one of the TCP flows was in the middle of FRTO algorithm (and then RTO is again triggered) 2) SACK reneging occurs during FRTO algorithm A simple solution is just to abort the previous FRTO when such obscure condition occurs... Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP] FRTO: Add missing ECN CWR sending to one of the responsesIlpo Järvinen2007-05-19
| | | | | | | | | | | | | | | | | The conservative spurious RTO response did not queue CWR even though the sending rate was lowered. Whenever reduction happens regardless of reason, CWR should be sent (forgetting to send it is not very fatal though). A better approach would be to queue CWR when one of the sending rate reducing responses (rate-halving one or this conservative response) is used already at RTO. Doing that would allow CWR to be sent along with the two new data segments that are sent during FRTO. However, it's a bit "racy" because userland could tune the response sysctl to a more aggressive one in between. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP] FRTO: RFC4138 allows Nagle override when new data must be sentIlpo Järvinen2007-04-30
| | | | | | | | | | | | | | This is a corner case where less than MSS sized new data thingie is awaiting in the send queue. For F-RTO to work correctly, a new data segment must be sent at certain point or F-RTO cannot be used at all. RFC4138 allows overriding of Nagle at that point. Implementation uses frto_counter states 2 and 3 to distinguish when Nagle override is needed. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP] FRTO: Delay skb available check until it's mandatoryIlpo Järvinen2007-04-30
| | | | | | | | No new data is needed until the first ACK comes, so no need to check for application limitedness until then. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Congestion control API update.Stephen Hemminger2007-04-26
| | | | | | | | | | | Do some simple changes to make congestion control API faster/cleaner. * use ktime_t rather than timeval * merge rtt sampling into existing ack callback this means one indirect call versus two per ack. * use flags bits to store options/settings Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Sed magic converts func(sk, tp, ...) -> func(sk, ...)Ilpo Järvinen2007-04-26
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This is (mostly) automated change using magic: sed -e '/struct sock \*sk/ N' -e '/struct sock \*sk/ N' -e '/struct sock \*sk/ N' -e '/struct sock \*sk/ N' -e 's|struct sock \*sk,[\n\t ]*struct tcp_sock \*tp\([^{]*\n{\n\)| struct sock \*sk\1\tstruct tcp_sock *tp = tcp_sk(sk);\n|g' -e 's|struct sock \*sk, struct tcp_sock \*tp| struct sock \*sk|g' -e 's|sk, tp\([^-]\)|sk\1|g' Fixed four unused variable (tp) warnings that were introduced. In addition, manually added newlines after local variables and tweaked function arguments positioning. $ gcc --version gcc (GCC) 4.1.1 20060525 (Red Hat 4.1.1-1) ... $ codiff -fV built-in.o.old built-in.o.new net/ipv4/route.c: rt_cache_flush | +14 1 function changed, 14 bytes added net/ipv4/tcp.c: tcp_setsockopt | -5 tcp_sendpage | -25 tcp_sendmsg | -16 3 functions changed, 46 bytes removed net/ipv4/tcp_input.c: tcp_try_undo_recovery | +3 tcp_try_undo_dsack | +2 tcp_mark_head_lost | -12 tcp_ack | -15 tcp_event_data_recv | -32 tcp_rcv_state_process | -10 tcp_rcv_established | +1 7 functions changed, 6 bytes added, 69 bytes removed, diff: -63 net/ipv4/tcp_output.c: update_send_head | -9 tcp_transmit_skb | +19 tcp_cwnd_validate | +1 tcp_write_wakeup | -17 __tcp_push_pending_frames | -25 tcp_push_one | -8 tcp_send_fin | -4 7 functions changed, 20 bytes added, 63 bytes removed, diff: -43 built-in.o.new: 18 functions changed, 40 bytes added, 178 bytes removed, diff: -138 Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [NET]: cleanup extra semicolonsStephen Hemminger2007-04-26
| | | | | | | | | | | Spring cleaning time... There seems to be a lot of places in the network code that have extra bogus semicolons after conditionals. Most commonly is a bogus semicolon after: switch() { } Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org> Signed-off-by: David S. Miller <davem@davemloft.net>
* [NET]: Treat CHECKSUM_PARTIAL as CHECKSUM_UNNECESSARYHerbert Xu2007-04-26
| | | | | | | | | When a transmitted packet is looped back directly, CHECKSUM_PARTIAL maps to the semantics of CHECKSUM_UNNECESSARY. Therefore we should treat it as such in the stack. Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: David S. Miller <davem@davemloft.net>
* [SK_BUFF]: Introduce skb_transport_header(skb)Arnaldo Carvalho de Melo2007-04-26
| | | | | | | | | For the places where we need a pointer to the transport header, it is still legal to touch skb->h.raw directly if just adding to, subtracting from or setting it to another layer header. Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* [SK_BUFF]: Introduce tcp_hdr(), remove skb->h.thArnaldo Carvalho de Melo2007-04-26
| | | | | Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* [SK_BUFF]: Introduce skb_set_transport_headerArnaldo Carvalho de Melo2007-04-26
| | | | | | | | For the cases where the transport header is being set to a offset from skb->data. Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* [SK_BUFF]: Introduce skb_set_network_headerArnaldo Carvalho de Melo2007-04-26
| | | | | | | For the cases where the network header is being set to a offset from skb->data. Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* [SK_BUFF]: Introduce skb_network_header()Arnaldo Carvalho de Melo2007-04-26
| | | | | | | | | For the places where we need a pointer to the network header, it is still legal to touch skb->nh.raw directly if just adding to, subtracting from or setting it to another layer header. Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* [SK_BUFF]: Introduce skb_mac_header()Arnaldo Carvalho de Melo2007-04-26
| | | | | | | | | | | | For the places where we need a pointer to the mac header, it is still legal to touch skb->mac.raw directly if just adding to, subtracting from or setting it to another layer header. This one also converts some more cases to skb_reset_mac_header() that my regex missed as it had no spaces before nor after '=', ugh. Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Use skb_set_mac_header in tcp_collapseArnaldo Carvalho de Melo2007-04-26
| | | | | Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Do the layer header setting in tcp_collapse relative to skb->dataArnaldo Carvalho de Melo2007-04-26
| | | | | | | | That is equal to skb->head before skb_reserve, to help in the layer header changes. Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: whitespace cleanupStephen Hemminger2007-04-26
| | | | | | | Add whitespace around keywords. Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Abstract out all write queue operations.David S. Miller2007-04-26
| | | | | | | This allows the write queue implementation to be changed, for example, to one which allows fast interval searching. Signed-off-by: David S. Miller <davem@davemloft.net>
* [NET]: Convert xtime.tv_sec to get_seconds()James Morris2007-04-26
| | | | | | | | Where appropriate, convert references to xtime.tv_sec to the get_seconds() helper function. Signed-off-by: James Morris <jmorris@namei.org> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: FRTO undo response falls back to ratehalving one if ECEdIlpo Järvinen2007-04-26
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Undoing ssthresh is disabled in fastretrans_alert whenever FLAG_ECE is set by clearing prior_ssthresh. The clearing does not protect FRTO because FRTO operates before fastretrans_alert. Moving the clearing of prior_ssthresh earlier seems to be a suboptimal solution to the FRTO case because then FLAG_ECE will cause a second ssthresh reduction in try_to_open (the first occurred when FRTO was entered). So instead, FRTO falls back immediately to the rate halving response, which switches TCP to CA_CWR state preventing the latter reduction of ssthresh. If the first ECE arrived before the ACK after which FRTO is able to decide RTO as spurious, prior_ssthresh is already cleared. Thus no undoing for ssthresh occurs. Besides, FLAG_ECE should be set also in the following ACKs resulting in rate halving response that sees TCP is already in CA_CWR, which again prevents an extra ssthresh reduction on that round-trip. If the first ECE arrived before RTO, ssthresh has already been adapted and prior_ssthresh remains cleared on entry because TCP is in CA_CWR (the same applies also to a case where FRTO is entered more than once and ECE comes in the middle). High_seq must not be touched after tcp_enter_cwr because CWR round-trip calculation depends on it. I believe that after this patch, FRTO should be ECN-safe and even able to take advantage of synergy benefits. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Complete icsk-to-local-variable change (in tcp_enter_cwr)Ilpo Järvinen2007-04-26
| | | | | | | | A local variable for icsk was created but this change was missing. Spotted by Jarek Poplawski. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Add two new spurious RTO responses to FRTOIlpo Järvinen2007-04-26
| | | | | | | | | | | | | | | | | New sysctl tcp_frto_response is added to select amongst these responses: - Rate halving based; reuses CA_CWR state (default) - Very conservative; used to be the only one available (=1) - Undo cwr; undoes ssthresh and cwnd reductions (=2) The response with rate halving requires a new parameter to tcp_enter_cwr because FRTO has already reduced ssthresh and doing a second reduction there has to be prevented. In addition, to keep things nice on 80 cols screen, a local variable was added. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Correct reordering detection change (no FRTO case)Ilpo Järvinen2007-04-26
| | | | | | | | | The reordering detection must work also when FRTO has not been used at all which was the original intention of mine, just the expression of the idea was flawed. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: SACK enhanced FRTOIlpo Järvinen2007-04-26
| | | | | | | | | | | | | | | | | | | Implements the SACK-enhanced FRTO given in RFC4138 using the variant given in Appendix B. RFC4138, Appendix B: "This means that in order to declare timeout spurious, the TCP sender must receive an acknowledgment for non-retransmitted segment between SND.UNA and RecoveryPoint in algorithm step 3. RecoveryPoint is defined in conservative SACK-recovery algorithm [RFC3517]" The basic version of the FRTO algorithm can still be used also when SACK is enabled. To enabled SACK-enhanced version, tcp_frto sysctl is set to 2. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Prevent reordering adjustments during FRTOIlpo Järvinen2007-04-26
| | | | | | | | | | | | To be honest, I'm not too sure how the reord stuff works in the first place but this seems necessary. When FRTO has been active, the one and only retransmission could be unnecessary but the state and sending order might not be what the sacktag code expects it to be (to work correctly). Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP] FRTO: Fake cwnd for ssthresh callbackIlpo Järvinen2007-04-26
| | | | | | | | | | | | | | | | | | TCP without FRTO would be in Loss state with small cwnd. FRTO, however, leaves cwnd (typically) to a larger value which causes ssthresh to become too large in case RTO is triggered again compared to what conventional recovery would do. Because consecutive RTOs result in only a single ssthresh reduction, RTO+cumulative ACK+RTO pattern is required to trigger this event. A large comment is included for congestion control module writers trying to figure out what CA_EVENT_FRTO handler should do because there exists a remote possibility of incompatibility between FRTO and module defined ssthresh functions. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP] FRTO: Reverse RETRANS bit clearing logicIlpo Järvinen2007-04-26
| | | | | | | | | | | | | | | | | | | | | | Previously RETRANS bits were cleared on the entry to FRTO. We postpone that into tcp_enter_frto_loss, which is really the place were the clearing should be done anyway. This allows simplification of the logic from a clearing loop to the head skb clearing only. Besides, the other changes made in the previous patches to tcp_use_frto made it impossible for the non-SACKed FRTO to be entered if other than the head has been rexmitted. With SACK-enhanced FRTO (and Appendix B), however, there can be a number retransmissions in flight when RTO expires (same thing could happen before this patchset also with non-SACK FRTO). To not introduce any jumpiness into the packet counting during FRTO, instead of clearing RETRANS bits from skbs during entry, do it later on. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP] FRTO: Entry is allowed only during (New)Reno like recoveryIlpo Järvinen2007-04-26
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This interpretation comes from RFC4138: "If the sender implements some loss recovery algorithm other than Reno or NewReno [FHG04], the F-RTO algorithm SHOULD NOT be entered when earlier fast recovery is underway." I think the RFC means to say (especially in the light of Appendix B) that ...recovery is underway (not just fast recovery) or was underway when it was interrupted by an earlier (F-)RTO that hasn't yet been resolved (snd_una has not advanced enough). Thus, my interpretation is that whenever TCP has ever retransmitted other than head, basic version cannot be used because then the order assumptions which are used as FRTO basis do not hold. NewReno has only the head segment retransmitted at a time. Therefore, walk up to the segment that has not been SACKed, if that segment is not retransmitted nor anything before it, we know for sure, that nothing after the non-SACKed segment should be either. This assumption is valid because TCPCB_EVER_RETRANS does not leave holes but each non-SACKed segment is rexmitted in-order. Check for retrans_out > 1 avoids more expensive walk through the skb list, as we can know the result beforehand: F-RTO will not be allowed. SACKed skb can turn into non-SACked only in the extremely rare case of SACK reneging, in this case we might fail to detect retransmissions if there were them for any other than head. To get rid of that feature, whole rexmit queue would have to be walked (always) or FRTO should be prevented when SACK reneging happens. Of course RTO should still trigger after reneging which makes this issue even less likely to show up. And as long as the response is as conservative as it's now, nothing bad happens even then. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Prevent unrelated cwnd adjustment while using FRTOIlpo Järvinen2007-04-26
| | | | | | | | | | FRTO controls cwnd when it still processes the ACK input or it has just reverted back to conventional RTO recovery; the normal rules apply when FRTO has reverted to standard congestion control. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP] FRTO: frto_counter modulo-op converted to two assignmentsIlpo Järvinen2007-04-26
| | | | | Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP]: Don't enter to fast recovery while using FRTOIlpo Järvinen2007-04-26
| | | | | | | | | | | | | | Because TCP is not in Loss state during FRTO recovery, fast recovery could be triggered by accident. Non-SACK FRTO is more robust than not yet included SACK-enhanced version (that can receiver high number of duplicate ACKs with SACK blocks during FRTO), at least with unidirectional transfers, but under extraordinary patterns fast recovery can be incorrectly triggered, e.g., Data loss+ACK losses => cumulative ACK with enough SACK blocks to meet sacked_out >= dupthresh condition). Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP] FRTO: Response should reset also snd_cwnd_cntIlpo Järvinen2007-04-26
| | | | | | | | Since purpose is to reduce CWND, we prevent immediate growth. This is not a major issue nor is "the correct way" specified anywhere. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP] FRTO: fixes fallback to conventional recoveryIlpo Järvinen2007-04-26
| | | | | | | | | | | | | | | | | | | | | | | | | | The FRTO detection did not care how ACK pattern affects to cwnd calculation of the conventional recovery. This caused incorrect setting of cwnd when the fallback becames necessary. The knowledge tcp_process_frto() has about the incoming ACK is now passed on to tcp_enter_frto_loss() in allowed_segments parameter that gives the number of segments that must be added to packets-in-flight while calculating the new cwnd. Instead of snd_una we use FLAG_DATA_ACKED in duplicate ACK detection because RFC4138 states (in Section 2.2): If the first acknowledgment after the RTO retransmission does not acknowledge all of the data that was retransmitted in step 1, the TCP sender reverts to the conventional RTO recovery. Otherwise, a malicious receiver acknowledging partial segments could cause the sender to declare the timeout spurious in a case where data was lost. If the next ACK after RTO is duplicate, we do not retransmit anything, which is equal to what conservative conventional recovery does in such case. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP] FRTO: Ignore some uninteresting ACKsIlpo Järvinen2007-04-26
| | | | | | | | | Handles RFC4138 shortcoming (in step 2); it should also have case c) which ignores ACKs that are not duplicates nor advance window (opposite dir data, winupdate). Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP] FRTO: Use Disorder state during operation instead of OpenIlpo Järvinen2007-04-26
| | | | | | | | | | | | | | | | | | | | | | | Retransmission counter assumptions are to be changed. Forcing reason to do this exist: Using sysctl in check would be racy as soon as FRTO starts to ignore some ACKs (doing that in the following patches). Userspace may disable it at any moment giving nice oops if timing is right. frto_counter would be inaccessible from userspace, but with SACK enhanced FRTO retrans_out can include other than head, and possibly leaving it non-zero after spurious RTO, boom again. Luckily, solution seems rather simple: never go directly to Open state but use Disorder instead. This does not really change much, since TCP could anyway change its state to Disorder during FRTO using path tcp_fastretrans_alert -> tcp_try_to_open (e.g., when a SACK block makes ACK dubious). Besides, Disorder seems to be the state where TCP should be if not recovering (in Recovery or Loss state) while having some retransmissions in-flight (see tcp_try_to_open), which is exactly what happens with FRTO. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP] FRTO: Consecutive RTOs keep prior_ssthresh and ssthreshIlpo Järvinen2007-04-26
| | | | | | | | | | | | | | In case a latency spike causes more than one RTO, the later should not cause the already reduced ssthresh to propagate into the prior_ssthresh since FRTO declares all such RTOs spurious at once or none of them. In treating of ssthresh, we mimic what tcp_enter_loss() does. The previous state (in frto_counter) must be available until we have checked it in tcp_enter_frto(), and also ACK information flag in process_frto(). Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP] FRTO: Comment cleanup & improvementIlpo Järvinen2007-04-26
| | | | | | | | | | | | Moved comments out from the body of process_frto() to the head (preferred way; see Documentation/CodingStyle). Bonus: it's much easier to read in this compacted form. FRTO algorithm and implementation is described in greater detail. For interested reader, more information is available in RFC4138. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
* [TCP] FRTO: Moved tcp_use_frto from tcp.h to tcp_input.cIlpo Järvinen2007-04-26
| | | | | | | In addition, removed inline. Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> Signed-off-by: David S. Miller <davem@davemloft.net>
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