| Message ID | 1408705410-28558-3-git-send-email-dborkman@redhat.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
On Fri, Aug 22, 2014 at 01:03:30PM +0200, Daniel Borkmann wrote: > In SCTP, selection of active (T.ACT) and retransmission (T.RET) > transports is being done whenever transport control operations > (UP, DOWN, PF, ...) are engaged through sctp_assoc_control_transport(). > > Commits 4c47af4d5eb2 ("net: sctp: rework multihoming retransmission > path selection to rfc4960") and a7288c4dd509 ("net: sctp: improve > sctp_select_active_and_retran_path selection") have both improved > it towards a more fine-grained and optimal path selection. > > Currently, the selection algorithm for T.ACT and T.RET is as follows: > > 1) Elect the two most recently used ACTIVE transports T1, T2 for > T.ACT, T.RET, where T.ACT<-T1 and T1 is most recently used > 2) In case primary path T.PRI not in {T1, T2} but ACTIVE, set > T.ACT<-T.PRI and T.RET<-T1 > 3) If only T1 is ACTIVE from the set, set T.ACT<-T1 and T.RET<-T1 > 4) If none is ACTIVE, set T.ACT<-best(T.PRI, T.RET, T3) where > T3 is the most recently used (if avail) in PF, set T.RET<-T.PRI > > Prior to above commits, 4) was simply a camp on T.ACT<-T.PRI and > T.RET<-T.PRI, ignoring possible paths in PF. Camping on T.PRI is > still slightly suboptimal as it can lead to the following scenario: > > Setup: > <A> <B> > T1: p1p1 (10.0.10.10) <==> .'`) <==> p1p1 (10.0.10.12) <= T.PRI > T2: p1p2 (10.0.10.20) <==> (_ . ) <==> p1p2 (10.0.10.22) > > net.sctp.rto_min = 1000 > net.sctp.path_max_retrans = 2 > net.sctp.pf_retrans = 0 > net.sctp.hb_interval = 1000 > > T.PRI is permanently down, T2 is put briefly into PF state (e.g. due to > link flapping). Here, the first time transmission is sent over PF path > T2 as it's the only non-INACTIVE path, but the retransmitted data-chunks > are sent over the INACTIVE path T1 (T.PRI), which is not good. > > After the patch, it's choosing better transports in both cases by > modifying step 4): > > 4) If none is ACTIVE, set T.ACT_new<-best(T.ACT_old, T3) where T3 is > the most recently used (if avail) in PF, set T.RET<-T.ACT_new > > This will still select a best possible path in PF if available (which > can also include T.PRI/T.RET), and set both T.ACT/T.RET to it. > > In case sctp_assoc_control_transport() *just* put T.ACT_old into INACTIVE > as it transitioned from ACTIVE->PF->INACTIVE and stays in INACTIVE just > for a very short while before going back ACTIVE, it will guarantee that > this path will be reselected for T.ACT/T.RET since T3 (PF) is not > available. > > Previously, this was not possible, as we would only select between T.PRI > and T.RET, and a possible T3 would be NULL due to the fact that we have > just transitioned T3 in sctp_assoc_control_transport() from PF->INACTIVE > and would select a suboptimal path when T.PRI/T.RET have worse properties. > > In the case that T.ACT_old permanently went to INACTIVE during this > transition and there's no PF path available, plus T.PRI and T.RET are > INACTIVE as well, we would now camp on T.ACT_old, but if everything is > being INACTIVE there's really not much we can do except hoping for a > successful HB to bring one of the transports back up again and, thus > cause a new selection through sctp_assoc_control_transport(). > > Now both tests work fine: > > Case 1: > > 1. T1 S(ACTIVE) T.ACT > T2 S(ACTIVE) T.RET > > 2. T1 S(ACTIVE) T.ACT, T.RET > T2 S(PF) > > 3. T1 S(ACTIVE) T.ACT, T.RET > T2 S(INACTIVE) > > 5. T1 S(PF) T.ACT, T.RET > T2 S(INACTIVE) > > [ 5.1 T1 S(INACTIVE) T.ACT, T.RET > T2 S(INACTIVE) ] > > 6. T1 S(ACTIVE) T.ACT, T.RET > T2 S(INACTIVE) > > 7. T1 S(ACTIVE) T.ACT > T2 S(ACTIVE) T.RET > > Case 2: > > 1. T1 S(ACTIVE) T.ACT > T2 S(ACTIVE) T.RET > > 2. T1 S(PF) > T2 S(ACTIVE) T.ACT, T.RET > > 3. T1 S(INACTIVE) > T2 S(ACTIVE) T.ACT, T.RET > > 5. T1 S(INACTIVE) > T2 S(PF) T.ACT, T.RET > > [ 5.1 T1 S(INACTIVE) > T2 S(INACTIVE) T.ACT, T.RET ] > > 6. T1 S(INACTIVE) > T2 S(ACTIVE) T.ACT, T.RET > > 7. T1 S(ACTIVE) T.ACT > T2 S(ACTIVE) T.RET > > Signed-off-by: Daniel Borkmann <dborkman@redhat.com> > --- > net/sctp/associola.c | 9 +++------ > 1 file changed, 3 insertions(+), 6 deletions(-) > > diff --git a/net/sctp/associola.c b/net/sctp/associola.c > index 104fae4..a88b852 100644 > --- a/net/sctp/associola.c > +++ b/net/sctp/associola.c > @@ -1356,14 +1356,11 @@ static void sctp_select_active_and_retran_path(struct sctp_association *asoc) > trans_sec = trans_pri; > > /* If we failed to find a usable transport, just camp on the > - * primary or retran, even if they are inactive, if possible > - * pick a PF iff it's the better choice. > + * active or pick a PF iff it's the better choice. > */ > if (trans_pri == NULL) { > - trans_pri = sctp_trans_elect_best(asoc->peer.primary_path, > - asoc->peer.retran_path); > - trans_pri = sctp_trans_elect_best(trans_pri, trans_pf); > - trans_sec = asoc->peer.primary_path; > + trans_pri = sctp_trans_elect_best(asoc->peer.active_path, trans_pf); > + trans_sec = trans_pri; > } > > /* Set the active and retran transports. */ > -- > 1.7.11.7 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-sctp" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Acked-by: Neil Horman <nhorman@tuxdriver.com> -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 08/22/2014 07:03 AM, Daniel Borkmann wrote: > In SCTP, selection of active (T.ACT) and retransmission (T.RET) > transports is being done whenever transport control operations > (UP, DOWN, PF, ...) are engaged through sctp_assoc_control_transport(). > > Commits 4c47af4d5eb2 ("net: sctp: rework multihoming retransmission > path selection to rfc4960") and a7288c4dd509 ("net: sctp: improve > sctp_select_active_and_retran_path selection") have both improved > it towards a more fine-grained and optimal path selection. > .. snip excellent changelog description ... > T2 S(ACTIVE) T.RET > > Signed-off-by: Daniel Borkmann <dborkman@redhat.com> Acked-by: Vlad Yasevich <vyasevich@gmail.com> > --- > net/sctp/associola.c | 9 +++------ > 1 file changed, 3 insertions(+), 6 deletions(-) > > diff --git a/net/sctp/associola.c b/net/sctp/associola.c > index 104fae4..a88b852 100644 > --- a/net/sctp/associola.c > +++ b/net/sctp/associola.c > @@ -1356,14 +1356,11 @@ static void sctp_select_active_and_retran_path(struct sctp_association *asoc) > trans_sec = trans_pri; > > /* If we failed to find a usable transport, just camp on the > - * primary or retran, even if they are inactive, if possible > - * pick a PF iff it's the better choice. > + * active or pick a PF iff it's the better choice. > */ > if (trans_pri == NULL) { > - trans_pri = sctp_trans_elect_best(asoc->peer.primary_path, > - asoc->peer.retran_path); > - trans_pri = sctp_trans_elect_best(trans_pri, trans_pf); > - trans_sec = asoc->peer.primary_path; > + trans_pri = sctp_trans_elect_best(asoc->peer.active_path, trans_pf); > + trans_sec = trans_pri; > } > > /* Set the active and retran transports. */ > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/sctp/associola.c b/net/sctp/associola.c index 104fae4..a88b852 100644 --- a/net/sctp/associola.c +++ b/net/sctp/associola.c @@ -1356,14 +1356,11 @@ static void sctp_select_active_and_retran_path(struct sctp_association *asoc) trans_sec = trans_pri; /* If we failed to find a usable transport, just camp on the - * primary or retran, even if they are inactive, if possible - * pick a PF iff it's the better choice. + * active or pick a PF iff it's the better choice. */ if (trans_pri == NULL) { - trans_pri = sctp_trans_elect_best(asoc->peer.primary_path, - asoc->peer.retran_path); - trans_pri = sctp_trans_elect_best(trans_pri, trans_pf); - trans_sec = asoc->peer.primary_path; + trans_pri = sctp_trans_elect_best(asoc->peer.active_path, trans_pf); + trans_sec = trans_pri; } /* Set the active and retran transports. */
In SCTP, selection of active (T.ACT) and retransmission (T.RET) transports is being done whenever transport control operations (UP, DOWN, PF, ...) are engaged through sctp_assoc_control_transport(). Commits 4c47af4d5eb2 ("net: sctp: rework multihoming retransmission path selection to rfc4960") and a7288c4dd509 ("net: sctp: improve sctp_select_active_and_retran_path selection") have both improved it towards a more fine-grained and optimal path selection. Currently, the selection algorithm for T.ACT and T.RET is as follows: 1) Elect the two most recently used ACTIVE transports T1, T2 for T.ACT, T.RET, where T.ACT<-T1 and T1 is most recently used 2) In case primary path T.PRI not in {T1, T2} but ACTIVE, set T.ACT<-T.PRI and T.RET<-T1 3) If only T1 is ACTIVE from the set, set T.ACT<-T1 and T.RET<-T1 4) If none is ACTIVE, set T.ACT<-best(T.PRI, T.RET, T3) where T3 is the most recently used (if avail) in PF, set T.RET<-T.PRI Prior to above commits, 4) was simply a camp on T.ACT<-T.PRI and T.RET<-T.PRI, ignoring possible paths in PF. Camping on T.PRI is still slightly suboptimal as it can lead to the following scenario: Setup: <A> <B> T1: p1p1 (10.0.10.10) <==> .'`) <==> p1p1 (10.0.10.12) <= T.PRI T2: p1p2 (10.0.10.20) <==> (_ . ) <==> p1p2 (10.0.10.22) net.sctp.rto_min = 1000 net.sctp.path_max_retrans = 2 net.sctp.pf_retrans = 0 net.sctp.hb_interval = 1000 T.PRI is permanently down, T2 is put briefly into PF state (e.g. due to link flapping). Here, the first time transmission is sent over PF path T2 as it's the only non-INACTIVE path, but the retransmitted data-chunks are sent over the INACTIVE path T1 (T.PRI), which is not good. After the patch, it's choosing better transports in both cases by modifying step 4): 4) If none is ACTIVE, set T.ACT_new<-best(T.ACT_old, T3) where T3 is the most recently used (if avail) in PF, set T.RET<-T.ACT_new This will still select a best possible path in PF if available (which can also include T.PRI/T.RET), and set both T.ACT/T.RET to it. In case sctp_assoc_control_transport() *just* put T.ACT_old into INACTIVE as it transitioned from ACTIVE->PF->INACTIVE and stays in INACTIVE just for a very short while before going back ACTIVE, it will guarantee that this path will be reselected for T.ACT/T.RET since T3 (PF) is not available. Previously, this was not possible, as we would only select between T.PRI and T.RET, and a possible T3 would be NULL due to the fact that we have just transitioned T3 in sctp_assoc_control_transport() from PF->INACTIVE and would select a suboptimal path when T.PRI/T.RET have worse properties. In the case that T.ACT_old permanently went to INACTIVE during this transition and there's no PF path available, plus T.PRI and T.RET are INACTIVE as well, we would now camp on T.ACT_old, but if everything is being INACTIVE there's really not much we can do except hoping for a successful HB to bring one of the transports back up again and, thus cause a new selection through sctp_assoc_control_transport(). Now both tests work fine: Case 1: 1. T1 S(ACTIVE) T.ACT T2 S(ACTIVE) T.RET 2. T1 S(ACTIVE) T.ACT, T.RET T2 S(PF) 3. T1 S(ACTIVE) T.ACT, T.RET T2 S(INACTIVE) 5. T1 S(PF) T.ACT, T.RET T2 S(INACTIVE) [ 5.1 T1 S(INACTIVE) T.ACT, T.RET T2 S(INACTIVE) ] 6. T1 S(ACTIVE) T.ACT, T.RET T2 S(INACTIVE) 7. T1 S(ACTIVE) T.ACT T2 S(ACTIVE) T.RET Case 2: 1. T1 S(ACTIVE) T.ACT T2 S(ACTIVE) T.RET 2. T1 S(PF) T2 S(ACTIVE) T.ACT, T.RET 3. T1 S(INACTIVE) T2 S(ACTIVE) T.ACT, T.RET 5. T1 S(INACTIVE) T2 S(PF) T.ACT, T.RET [ 5.1 T1 S(INACTIVE) T2 S(INACTIVE) T.ACT, T.RET ] 6. T1 S(INACTIVE) T2 S(ACTIVE) T.ACT, T.RET 7. T1 S(ACTIVE) T.ACT T2 S(ACTIVE) T.RET Signed-off-by: Daniel Borkmann <dborkman@redhat.com> --- net/sctp/associola.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-)