On 04/14/2014 03:45 PM, Daniel Borkmann wrote:
> 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@xxxxxxxxxxxx>
> Reported-by: Dongsheng Song <dongsheng.song@xxxxxxxxx>
> Reported-by: Fengguang Wu <fengguang.wu@xxxxxxxxx>
> Tested-by: Peter Butler <pbutler@xxxxxxxxxxxx>
> Signed-off-by: Daniel Borkmann <dborkman@xxxxxxxxxx>
> Cc: Matija Glavinic Pecotic <matija.glavinic-pecotic.ext@xxxxxxx>
> Cc: Alexander Sverdlin <alexander.sverdlin@xxxxxxx>
> Cc: Vlad Yasevich <vyasevich@xxxxxxxxx>
Acked-by: Vlad Yasevich <vyasevich@xxxxxxxxx>
The base approach is sound. The idea is to calculate rwnd based
on receiver buffer available. The algorithm chosen however, is
gives a much higher preference to small data and penalizes large
data transfers. We need to figure our something else here..
-vlad
> ---
> As commit ef2820a735f7 affects kernels with 3.11 and onwards, this
> needs a rework by Matija for net-next again, so that this fix can
> go back to -stable and restore performance for 3.11-3.15 kernels.
>
> 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(-)
>
> diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
> index 6ee76c8..d992ca3 100644
> --- 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_association *old,
> __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 *,
> diff --git a/net/sctp/associola.c b/net/sctp/associola.c
> index 4f6d6f9..39579c3 100644
> --- a/net/sctp/associola.c
> +++ b/net/sctp/associola.c
> @@ -1395,35 +1395,44 @@ static inline bool sctp_peer_needs_update(struct sctp_association *asoc)
> 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 "
> @@ -1445,6 +1454,45 @@ void sctp_assoc_rwnd_update(struct sctp_association *asoc, bool update_peer)
> }
> }
>
> +/* 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.
> diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
> index 01e0024..ae9fbeb 100644
> --- a/net/sctp/sm_statefuns.c
> +++ b/net/sctp/sm_statefuns.c
> @@ -6178,7 +6178,7 @@ static int sctp_eat_data(const struct sctp_association *asoc,
> * 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
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index e13519e..ff20e2d 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -2115,6 +2115,12 @@ static int sctp_recvmsg(struct kiocb *iocb, struct sock *sk,
> 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))
> diff --git a/net/sctp/ulpevent.c b/net/sctp/ulpevent.c
> index 8d198ae..85c6465 100644
> --- a/net/sctp/ulpevent.c
> +++ b/net/sctp/ulpevent.c
> @@ -989,7 +989,7 @@ static void sctp_ulpevent_receive_data(struct sctp_ulpevent *event,
> 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(struct sctp_ulpevent *event)
> {
> 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(struct sctp_ulpevent *event)
> }
>
> 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)
>
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