[PATCH 3.14 077/140] Revert "net: sctp: Fix a_rwnd/rwnd management to reflect real state of the receivers buffer"

Greg Kroah-Hartman
2014-05-29T04:35:33Z

From: Daniel Borkmann <dborkman@redhat.com>

[ Upstream commit 362d52040c71f6e8d8158be48c812d7729cb8df1 ]

This reverts commit ef2820a735f7 ("net: sctp: Fix a_rwnd/rwnd management
to reflect real state of the receiver's buffer") as it introduced a
serious performance regression on SCTP over IPv4 and IPv6, though a not
as dramatic on the latter. Measurements are on 10Gbit/s with ixgbe NICs.

Current state:

[root@Lab200slot2 ~]# iperf3 --sctp -4 -c 192.168.241.3 -V -l 1452 -t 60
iperf version 3.0.1 (10 January 2014)
Linux Lab200slot2 3.14.0 #1 SMP Thu Apr 3 23:18:29 EDT 2014 x86_64
Time: Fri, 11 Apr 2014 17:56:21 GMT
Connecting to host 192.168.241.3, port 5201
Cookie: Lab200slot2.1397238981.812898.548918
[ 4] local 192.168.241.2 port 38616 connected to 192.168.241.3 port 5201
Starting Test: protocol: SCTP, 1 streams, 1452 byte blocks, omitting 0 seconds, 60 second test
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-1.09 sec 20.8 MBytes 161 Mbits/sec
[ 4] 1.09-2.13 sec 10.8 MBytes 86.8 Mbits/sec
[ 4] 2.13-3.15 sec 3.57 MBytes 29.5 Mbits/sec
[ 4] 3.15-4.16 sec 4.33 MBytes 35.7 Mbits/sec
[ 4] 4.16-6.21 sec 10.4 MBytes 42.7 Mbits/sec
[ 4] 6.21-6.21 sec 0.00 Bytes 0.00 bits/sec
[ 4] 6.21-7.35 sec 34.6 MBytes 253 Mbits/sec
[ 4] 7.35-11.45 sec 22.0 MBytes 45.0 Mbits/sec
[ 4] 11.45-11.45 sec 0.00 Bytes 0.00 bits/sec
[ 4] 11.45-11.45 sec 0.00 Bytes 0.00 bits/sec
[ 4] 11.45-11.45 sec 0.00 Bytes 0.00 bits/sec
[ 4] 11.45-12.51 sec 16.0 MBytes 126 Mbits/sec
[ 4] 12.51-13.59 sec 20.3 MBytes 158 Mbits/sec
[ 4] 13.59-14.65 sec 13.4 MBytes 107 Mbits/sec
[ 4] 14.65-16.79 sec 33.3 MBytes 130 Mbits/sec
[ 4] 16.79-16.79 sec 0.00 Bytes 0.00 bits/sec
[ 4] 16.79-17.82 sec 5.94 MBytes 48.7 Mbits/sec
(etc)

[root@Lab200slot2 ~]# iperf3 --sctp -6 -c 2001:db8:0:f101::1 -V -l 1400 -t 60
iperf version 3.0.1 (10 January 2014)
Linux Lab200slot2 3.14.0 #1 SMP Thu Apr 3 23:18:29 EDT 2014 x86_64
Time: Fri, 11 Apr 2014 19:08:41 GMT
Connecting to host 2001:db8:0:f101::1, port 5201
Cookie: Lab200slot2.1397243321.714295.2b3f7c
[ 4] local 2001:db8:0:f101::2 port 55804 connected to 2001:db8:0:f101::1 port 5201
Starting Test: protocol: SCTP, 1 streams, 1400 byte blocks, omitting 0 seconds, 60 second test
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-1.00 sec 169 MBytes 1.42 Gbits/sec
[ 4] 1.00-2.00 sec 201 MBytes 1.69 Gbits/sec
[ 4] 2.00-3.00 sec 188 MBytes 1.58 Gbits/sec
[ 4] 3.00-4.00 sec 174 MBytes 1.46 Gbits/sec
[ 4] 4.00-5.00 sec 165 MBytes 1.39 Gbits/sec
[ 4] 5.00-6.00 sec 199 MBytes 1.67 Gbits/sec
[ 4] 6.00-7.00 sec 163 MBytes 1.36 Gbits/sec
[ 4] 7.00-8.00 sec 174 MBytes 1.46 Gbits/sec
[ 4] 8.00-9.00 sec 193 MBytes 1.62 Gbits/sec
[ 4] 9.00-10.00 sec 196 MBytes 1.65 Gbits/sec
[ 4] 10.00-11.00 sec 157 MBytes 1.31 Gbits/sec
[ 4] 11.00-12.00 sec 175 MBytes 1.47 Gbits/sec
[ 4] 12.00-13.00 sec 192 MBytes 1.61 Gbits/sec
[ 4] 13.00-14.00 sec 199 MBytes 1.67 Gbits/sec
(etc)

After patch:

[root@Lab200slot2 ~]# iperf3 --sctp -4 -c 192.168.240.3 -V -l 1452 -t 60
iperf version 3.0.1 (10 January 2014)
Linux Lab200slot2 3.14.0+ #1 SMP Mon Apr 14 12:06:40 EDT 2014 x86_64
Time: Mon, 14 Apr 2014 16:40:48 GMT
Connecting to host 192.168.240.3, port 5201
Cookie: Lab200slot2.1397493648.413274.65e131
[ 4] local 192.168.240.2 port 50548 connected to 192.168.240.3 port 5201
Starting Test: protocol: SCTP, 1 streams, 1452 byte blocks, omitting 0 seconds, 60 second test
[ ID] Interval Transfer Bandwidth
[ 4] 0.00-1.00 sec 240 MBytes 2.02 Gbits/sec
[ 4] 1.00-2.00 sec 239 MBytes 2.01 Gbits/sec
[ 4] 2.00-3.00 sec 240 MBytes 2.01 Gbits/sec
[ 4] 3.00-4.00 sec 239 MBytes 2.00 Gbits/sec
[ 4] 4.00-5.00 sec 245 MBytes 2.05 Gbits/sec
[ 4] 5.00-6.00 sec 240 MBytes 2.01 Gbits/sec
[ 4] 6.00-7.00 sec 240 MBytes 2.02 Gbits/sec
[ 4] 7.00-8.00 sec 239 MBytes 2.01 Gbits/sec

With the reverted patch applied, the SCTP/IPv4 performance is back
to normal on latest upstream for IPv4 and IPv6 and has same throughput
as 3.4.2 test kernel, steady and interval reports are smooth again.

Fixes: ef2820a735f7 ("net: sctp: Fix a_rwnd/rwnd management to reflect real state of the receiver's buffer")
Reported-by: Peter Butler <pbutler@sonusnet.com>
Reported-by: Dongsheng Song <dongsheng.song@gmail.com>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Tested-by: Peter Butler <pbutler@sonusnet.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Cc: Matija Glavinic Pecotic <matija.glavinic-pecotic.ext@nsn.com>
Cc: Alexander Sverdlin <alexander.sverdlin@nsn.com>
Cc: Vlad Yasevich <vyasevich@gmail.com>
Acked-by: Vlad Yasevich <vyasevich@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/net/sctp/structs.h | 14 +++++++
net/sctp/associola.c | 82 +++++++++++++++++++++++++++++++++++----------
net/sctp/sm_statefuns.c | 2 -
net/sctp/socket.c | 6 +++
net/sctp/ulpevent.c | 8 +---
5 files changed, 87 insertions(+), 25 deletions(-)

--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -1653,6 +1653,17 @@ struct sctp_association {
/* This is the last advertised value of rwnd over a SACK chunk. */
__u32 a_rwnd;

+ /* Number of bytes by which the rwnd has slopped. The rwnd is allowed
+ * to slop over a maximum of the association's frag_point.
+ */
+ __u32 rwnd_over;
+
+ /* Keeps treack of rwnd pressure. This happens when we have
+ * a window, but not recevie buffer (i.e small packets). This one
+ * is releases slowly (1 PMTU at a time ).
+ */
+ __u32 rwnd_press;
+
/* This is the sndbuf size in use for the association.
* This corresponds to the sndbuf size for the association,
* as specified in the sk->sndbuf.
@@ -1881,7 +1892,8 @@ void sctp_assoc_update(struct sctp_assoc
__u32 sctp_association_get_next_tsn(struct sctp_association *);

void sctp_assoc_sync_pmtu(struct sock *, struct sctp_association *);
-void sctp_assoc_rwnd_update(struct sctp_association *, bool);
+void sctp_assoc_rwnd_increase(struct sctp_association *, unsigned int);
+void sctp_assoc_rwnd_decrease(struct sctp_association *, unsigned int);
void sctp_assoc_set_primary(struct sctp_association *,
struct sctp_transport *);
void sctp_assoc_del_nonprimary_peers(struct sctp_association *,
--- a/net/sctp/associola.c
+++ b/net/sctp/associola.c
@@ -1396,35 +1396,44 @@ static inline bool sctp_peer_needs_updat
return false;
}

-/* Update asoc's rwnd for the approximated state in the buffer,
- * and check whether SACK needs to be sent.
- */
-void sctp_assoc_rwnd_update(struct sctp_association *asoc, bool update_peer)
+/* Increase asoc's rwnd by len and send any window update SACK if needed. */
+void sctp_assoc_rwnd_increase(struct sctp_association *asoc, unsigned int len)
{
- int rx_count;
struct sctp_chunk *sack;
struct timer_list *timer;

- if (asoc->ep->rcvbuf_policy)
- rx_count = atomic_read(&asoc->rmem_alloc);
- else
- rx_count = atomic_read(&asoc->base.sk->sk_rmem_alloc);
+ if (asoc->rwnd_over) {
+ if (asoc->rwnd_over >= len) {
+ asoc->rwnd_over -= len;
+ } else {
+ asoc->rwnd += (len - asoc->rwnd_over);
+ asoc->rwnd_over = 0;
+ }
+ } else {
+ asoc->rwnd += len;
+ }

- if ((asoc->base.sk->sk_rcvbuf - rx_count) > 0)
- asoc->rwnd = (asoc->base.sk->sk_rcvbuf - rx_count) >> 1;
- else
- asoc->rwnd = 0;
+ /* If we had window pressure, start recovering it
+ * once our rwnd had reached the accumulated pressure
+ * threshold. The idea is to recover slowly, but up
+ * to the initial advertised window.
+ */
+ if (asoc->rwnd_press && asoc->rwnd >= asoc->rwnd_press) {
+ int change = min(asoc->pathmtu, asoc->rwnd_press);
+ asoc->rwnd += change;
+ asoc->rwnd_press -= change;
+ }

- pr_debug("%s: asoc:%p rwnd=%u, rx_count=%d, sk_rcvbuf=%d\n",
- __func__, asoc, asoc->rwnd, rx_count,
- asoc->base.sk->sk_rcvbuf);
+ pr_debug("%s: asoc:%p rwnd increased by %d to (%u, %u) - %u\n",
+ __func__, asoc, len, asoc->rwnd, asoc->rwnd_over,
+ asoc->a_rwnd);

/* Send a window update SACK if the rwnd has increased by at least the
* minimum of the association's PMTU and half of the receive buffer.
* The algorithm used is similar to the one described in
* Section 4.2.3.3 of RFC 1122.
*/
- if (update_peer && sctp_peer_needs_update(asoc)) {
+ if (sctp_peer_needs_update(asoc)) {
asoc->a_rwnd = asoc->rwnd;

pr_debug("%s: sending window update SACK- asoc:%p rwnd:%u "
@@ -1446,6 +1455,45 @@ void sctp_assoc_rwnd_update(struct sctp_
}
}

+/* Decrease asoc's rwnd by len. */
+void sctp_assoc_rwnd_decrease(struct sctp_association *asoc, unsigned int len)
+{
+ int rx_count;
+ int over = 0;
+
+ if (unlikely(!asoc->rwnd || asoc->rwnd_over))
+ pr_debug("%s: association:%p has asoc->rwnd:%u, "
+ "asoc->rwnd_over:%u!\n", __func__, asoc,
+ asoc->rwnd, asoc->rwnd_over);
+
+ if (asoc->ep->rcvbuf_policy)
+ rx_count = atomic_read(&asoc->rmem_alloc);
+ else
+ rx_count = atomic_read(&asoc->base.sk->sk_rmem_alloc);
+
+ /* If we've reached or overflowed our receive buffer, announce
+ * a 0 rwnd if rwnd would still be positive. Store the
+ * the potential pressure overflow so that the window can be restored
+ * back to original value.
+ */
+ if (rx_count >= asoc->base.sk->sk_rcvbuf)
+ over = 1;
+
+ if (asoc->rwnd >= len) {
+ asoc->rwnd -= len;
+ if (over) {
+ asoc->rwnd_press += asoc->rwnd;
+ asoc->rwnd = 0;
+ }
+ } else {
+ asoc->rwnd_over = len - asoc->rwnd;
+ asoc->rwnd = 0;
+ }
+
+ pr_debug("%s: asoc:%p rwnd decreased by %d to (%u, %u, %u)\n",
+ __func__, asoc, len, asoc->rwnd, asoc->rwnd_over,
+ asoc->rwnd_press);
+}

/* Build the bind address list for the association based on info from the
* local endpoint and the remote peer.
--- a/net/sctp/sm_statefuns.c
+++ b/net/sctp/sm_statefuns.c
@@ -6178,7 +6178,7 @@ static int sctp_eat_data(const struct sc
* PMTU. In cases, such as loopback, this might be a rather
* large spill over.
*/
- if ((!chunk->data_accepted) && (!asoc->rwnd ||
+ if ((!chunk->data_accepted) && (!asoc->rwnd || asoc->rwnd_over ||
(datalen > asoc->rwnd + asoc->frag_point))) {

/* If this is the next TSN, consider reneging to make
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -2115,6 +2115,12 @@ static int sctp_recvmsg(struct kiocb *io
sctp_skb_pull(skb, copied);
skb_queue_head(&sk->sk_receive_queue, skb);

+ /* When only partial message is copied to the user, increase
+ * rwnd by that amount. If all the data in the skb is read,
+ * rwnd is updated when the event is freed.
+ */
+ if (!sctp_ulpevent_is_notification(event))
+ sctp_assoc_rwnd_increase(event->asoc, copied);
goto out;
} else if ((event->msg_flags & MSG_NOTIFICATION) ||
(event->msg_flags & MSG_EOR))
--- a/net/sctp/ulpevent.c
+++ b/net/sctp/ulpevent.c
@@ -989,7 +989,7 @@ static void sctp_ulpevent_receive_data(s
skb = sctp_event2skb(event);
/* Set the owner and charge rwnd for bytes received. */
sctp_ulpevent_set_owner(event, asoc);
- sctp_assoc_rwnd_update(asoc, false);
+ sctp_assoc_rwnd_decrease(asoc, skb_headlen(skb));

if (!skb->data_len)
return;
@@ -1011,7 +1011,6 @@ static void sctp_ulpevent_release_data(s
{
struct sk_buff *skb, *frag;
unsigned int len;
- struct sctp_association *asoc;

/* Current stack structures assume that the rcv buffer is
* per socket. For UDP style sockets this is not true as
@@ -1036,11 +1035,8 @@ static void sctp_ulpevent_release_data(s
}

done:
- asoc = event->asoc;
- sctp_association_hold(asoc);
+ sctp_assoc_rwnd_increase(event->asoc, len);
sctp_ulpevent_release_owner(event);
- sctp_assoc_rwnd_update(asoc, true);
- sctp_association_put(asoc);
}

static void sctp_ulpevent_release_frag_data(struct sctp_ulpevent *event)