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Re: [tipc-discussion] [net-next] tipc: smooth change between replicast and broadcast
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From: Jon M. <jon...@er...> - 2019-01-31 21:05:56
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Hi Hoang,
Nice job, but still a few things to improve. See below.
> -----Original Message-----
> From: Hoang Le <hoa...@de...>
> Sent: 29-Jan-19 04:22
> To: Jon Maloy <jon...@er...>; ma...@do...;
> yin...@wi...; tip...@li...
> Subject: [net-next] tipc: smooth change between replicast and broadcast
>
> Currently, a multicast stream may start out using replicast, because there are
> few destinations, and then it should ideally switch to L2/broadcast
> IGMP/multicast when the number of destinations grows beyond a certain
> limit. The opposite should happen when the number decreases below the
> limit.
>
> To eliminate the risk of message reordering caused by method change, a
> sending socket must stick to a previously selected method until it enters an
> idle period of 5 seconds. Means there is a 5 seconds pause in the traffic from
> the sender socket.
>
> In this fix, we allow such a switch between replicast and broadcast without a
> 5 seconds pause in the traffic.
>
> Solution is to send a dummy message with only the header, also with the SYN
> bit set, via broadcast/replicast. For the data message, the SYN bit set and
> sending via replicast/broadcast.
>
> Then, at receiving side any messages follow first SYN bit message (data or
> dummy), they will be hold in deferred queue until another pair (dummy or
> data) arrived.
>
> For compatibility reasons we have to introduce a new capability flag
> TIPC_MCAST_RBCTL to handle this new feature. Because of there is a
> dummy message sent out, then poll return empty at old machines.
>
> Signed-off-by: Jon Maloy <jon...@er...>
> Signed-off-by: Hoang Le <hoa...@de...>
> ---
> net/tipc/bcast.c | 116
> +++++++++++++++++++++++++++++++++++++++++++++-
> net/tipc/bcast.h | 5 ++
> net/tipc/core.c | 2 +
> net/tipc/core.h | 3 ++
> net/tipc/msg.h | 10 ++++
> net/tipc/node.c | 10 ++++
> net/tipc/node.h | 6 ++-
> net/tipc/socket.c | 10 ++++
> 8 files changed, 159 insertions(+), 3 deletions(-)
>
> diff --git a/net/tipc/bcast.c b/net/tipc/bcast.c index
> d8026543bf4c..e3a85227d4aa 100644
> --- a/net/tipc/bcast.c
> +++ b/net/tipc/bcast.c
> @@ -295,11 +295,15 @@ int tipc_mcast_xmit(struct net *net, struct
> sk_buff_head *pkts,
> struct tipc_mc_method *method, struct tipc_nlist *dests,
> u16 *cong_link_cnt)
> {
> - struct sk_buff_head inputq, localq;
> + struct sk_buff_head inputq, localq, tmpq;
> + bool rcast = method->rcast;
> + struct sk_buff *skb, *_skb;
> + struct tipc_msg *hdr, *_hdr;
> int rc = 0;
>
> skb_queue_head_init(&inputq);
> skb_queue_head_init(&localq);
> + skb_queue_head_init(&tmpq);
>
> /* Clone packets before they are consumed by next call */
> if (dests->local && !tipc_msg_reassemble(pkts, &localq)) { @@ -
> 309,6 +313,53 @@ int tipc_mcast_xmit(struct net *net, struct sk_buff_head
> *pkts,
> /* Send according to determined transmit method */
> if (dests->remote) {
> tipc_bcast_select_xmit_method(net, dests->remote,
> method);
I would suggest that you move the whole code block below into a separate function:
msg_set_is_rcast(hdr, method->rcast);
if (rcast != method->rcast)
tipc_mcast_send_sync(net, skb_peek(pkts));
This function sets the SYN bit in the packet header, then copies that header into a dummy header, inverts the is_rcast bit in that header and sends it out via the appropriate method.
Note that this involves a small change: the real message is sent out via the selected method, the dummy message always via the other method, whichever it is.
> +
> + if (tipc_net(net)->capabilities & TIPC_MCAST_RBCTL) {
> + skb = skb_peek(pkts);
> + hdr = buf_msg(skb);
> +
> + if (msg_user(hdr) == MSG_FRAGMENTER)
> + hdr = msg_get_wrapped(hdr);
> + if (msg_type(hdr) != TIPC_MCAST_MSG)
> + goto xmit;
> +
> + msg_set_syn(hdr, 0);
> + msg_set_is_rcast(hdr, method->rcast);
> +
> + /* switch mode */
> + if (rcast != method->rcast) {
> + /* Build message's copied */
> + _skb = tipc_buf_acquire(MCAST_H_SIZE,
> + GFP_KERNEL);
> + if (!skb) {
> + rc = -ENOMEM;
> + goto exit;
> + }
> + skb_orphan(_skb);
> + skb_copy_to_linear_data(_skb, hdr,
> + MCAST_H_SIZE);
> +
> + /* Build dummy header */
> + _hdr = buf_msg(_skb);
> + msg_set_size(_hdr, MCAST_H_SIZE);
> + __skb_queue_tail(&tmpq, _skb);
> +
> + msg_set_syn(hdr, 1);
> + msg_set_syn(_hdr, 1);
> + msg_set_is_rcast(_hdr, rcast);
> + /* Prepare for 'synching' */
> + if (rcast)
> + tipc_rcast_xmit(net, &tmpq, dests,
> + cong_link_cnt);
> + else
> + tipc_bcast_xmit(net, &tmpq,
> + cong_link_cnt);
> +
> + /* This queue should normally be empty by
> now */
> + __skb_queue_purge(&tmpq);
> + }
> + }
> +xmit:
> if (method->rcast)
> rc = tipc_rcast_xmit(net, pkts, dests, cong_link_cnt);
> else
> @@ -576,3 +627,66 @@ void tipc_nlist_purge(struct tipc_nlist *nl)
> nl->remote = 0;
> nl->local = false;
> }
> +
> +void tipc_mcast_filter_msg(struct sk_buff_head *defq,
> + struct sk_buff_head *inputq)
> +{
> + struct sk_buff *skb, *_skb;
> + struct tipc_msg *hdr, *_hdr;
> + u32 node, port, _node, _port;
> + bool match = false;
If you put in the following lines here we will save some instruction cycles:
hdr = buf_msg(skb_peek(inputq));
if (likely(!msg_is_syn(hdr) && skb_queue_empty(defq)))
return;
After all this will be the case in the vast majority of cases. It is safe to just peek the queue and access, since inputq never can be empty.
> +
> + skb = __skb_dequeue(inputq);
> + if (!skb)
> + return;
> +
> + hdr = buf_msg(skb);
> + node = msg_orignode(hdr);
> + port = msg_origport(hdr);
> +
> + /* Find a peer port if its existing in defer queue */
> + while ((_skb = skb_peek(defq))) {
> + _hdr = buf_msg(_skb);
> + _node = msg_orignode(_hdr);
> + _port = msg_origport(_hdr);
> +
> + if (_node != node)
> + continue;
> + if (_port != port)
> + continue;
> +
> + if (!match) {
> + if (msg_is_syn(hdr) &&
> + msg_is_rcast(hdr) != msg_is_rcast(_hdr)) {
> + __skb_dequeue(defq);
> + if (msg_data_sz(hdr)) {
> + __skb_queue_tail(inputq, skb);
> + kfree_skb(_skb);
> + } else {
> + __skb_queue_tail(inputq, _skb);
> + kfree_skb(skb);
> + }
> + match = true;
> + } else {
> + break;
> + }
> + } else {
> + if (msg_is_syn(_hdr))
> + return;
> + /* Dequeued to receive buffer */
> + __skb_dequeue(defq);
> + __skb_queue_tail(inputq, _skb);
> + }
> + }
> +
> + if (match)
> + return;
> +
> + if (msg_is_syn(hdr)) {
> + /* Enqueue and defer to next synching */
> + __skb_queue_tail(defq, skb);
> + } else {
> + /* Direct enqueued */
> + __skb_queue_tail(inputq, skb);
> + }
> +}
Above function is hard to follow and does not convince me. What if there are messages from many sources, and you find the match in the middle of the queue?
I suggest you break down the logics to smaller tasks, e.g., as follows (code compiles ok, but is untested):
void tipc_mcast_filter_msg(struct sk_buff_head *defq,
struct sk_buff_head *inputq)
{
struct sk_buff *skb, *_skb, *tmp;
struct tipc_msg *hdr, *_hdr;
bool match = false;
u32 node, port;
skb = skb_peek(inputq);
hdr = buf_msg(skb);
if (likely(!msg_is_syn(hdr) && skb_queue_empty(defq)))
return;
__skb_dequeue(inputq);
node = msg_orignode(hdr);
port = msg_origport(hdr);
/* Has the twin SYN message already arrived ? */
skb_queue_walk(defq, _skb) {
_hdr = buf_msg(_skb);
if (msg_orignode(_hdr) != node)
continue;
if (msg_origport(_hdr) != port)
continue;
match = true;
break;
}
if (!match)
return __skb_queue_tail(defq, skb);
if (!msg_is_syn(_hdr)) {
pr_warn_ratelimited("Non-sync mcast heads deferred queue\n");
__skb_queue_purge(defq);
return __skb_queue_tail(inputq, skb);
}
/* Non-SYN message from other link can be delivered right away */
if (!msg_is_syn(hdr)) {
if (msg_is_rcast(hdr) != msg_is_rcast(_hdr))
return __skb_queue_tail(inputq, skb);
else
return __skb_queue_tail(defq, skb);
}
/* Matching SYN messages => return the one with data, if any */
__skb_unlink(_skb, defq);
if (msg_data_sz(hdr)) {
kfree_skb(_skb);
__skb_queue_tail(inputq, skb);
} else {
kfree_skb(skb);
__skb_queue_tail(inputq, _skb);
}
/* Deliver subsequent non-SYN messages from same peer */
skb_queue_walk_safe(defq, _skb, tmp) {
_hdr = buf_msg(_skb);
if (msg_orignode(_hdr) != node)
continue;
if (msg_origport(_hdr) != port)
continue;
if (msg_is_syn(_hdr))
break;
__skb_unlink(_skb, defq);
__skb_queue_tail(inputq, _skb);
}
}
> diff --git a/net/tipc/bcast.h b/net/tipc/bcast.h index
> 751530ab0c49..165d88a503e4 100644
> --- a/net/tipc/bcast.h
> +++ b/net/tipc/bcast.h
> @@ -63,11 +63,13 @@ void tipc_nlist_del(struct tipc_nlist *nl, u32 node);
> /* Cookie to be used between socket and broadcast layer
> * @rcast: replicast (instead of broadcast) was used at previous xmit
> * @mandatory: broadcast/replicast indication was set by user
> + * @deferredq: defer queue to make message in order
> * @expires: re-evaluate non-mandatory transmit method if we are past this
> */
[...]
> @@ -383,6 +383,11 @@ static struct tipc_node *tipc_node_create(struct net
> *net, u32 addr,
> tipc_link_update_caps(l, capabilities);
> }
> write_unlock_bh(&n->lock);
> + /* Calculate cluster capabilities */
> + tn->capabilities = TIPC_NODE_CAPABILITIES;
> + list_for_each_entry_rcu(temp_node, &tn->node_list, list) {
> + tn->capabilities &= temp_node->capabilities;
> + }
Yes, you are right here. During a cluster upgrade a node can come back with new capabilities which also must be reflected in the cluster capabilities field.
Actually, I think it would be a good idea to add cluster capabilities as a separate patch. This makes this rather complex patch slightly smaller.
> goto exit;
> }
> n = kzalloc(sizeof(*n), GFP_ATOMIC);
> @@ -433,6 +438,11 @@ static struct tipc_node *tipc_node_create(struct net
> *net, u32 addr,
> break;
[...]
>
> @@ -817,6 +819,11 @@ static int tipc_sendmcast(struct socket *sock, struct
> tipc_name_seq *seq,
> &tsk->cong_link_cnt);
> }
>
> + /* Broadcast link is now free to choose method for next broadcast */
> + if (rc == 0) {
> + method->mandatory = false;
> + method->expires = jiffies;
> + }
No, we should leave the socket code as is, so we are sure it works with legacy nodes.
We should instead make tipc_bcast_select_input_method() slightly smarter:
static void tipc_bcast_select_xmit_method(struct net *net, int dests,
struct tipc_mc_method *method)
{
.......
/* Can current method be changed ? */
method->expires = jiffies + TIPC_METHOD_EXPIRE;
if (method->mandatory)
return;
if (!(tipc_net(net)->capabilities & TIPC_MCAST_RBCTL)) && time_before(jiffies, exp))
return;
/* Determine method to use now */
method->rcast = dests <= bb->bc_threshold;
}
I.e., we respect the 'mandatory' setting, because we need that for group_cast wo work correctly, but we override 'method->expire' if the cluster capabilities says that all nodes support MCAST_RBCTL.
Combined with the patch where we add forced BCAST or REPLICAST (make sure you add this patch on top of that one) I think we have a achieved a pretty smart and adaptive multicast subsystem.
BR
///jon
> tipc_nlist_purge(&dsts);
>
> return rc ? rc : dlen;
> @@ -2157,6 +2164,9 @@ static void tipc_sk_filter_rcv(struct sock *sk, struct
> sk_buff *skb,
> if (unlikely(grp))
> tipc_group_filter_msg(grp, &inputq, xmitq);
>
> + if (msg_type(hdr) == TIPC_MCAST_MSG)
> + tipc_mcast_filter_msg(&tsk->mc_method.deferredq,
> &inputq);
> +
> /* Validate and add to receive buffer if there is space */
> while ((skb = __skb_dequeue(&inputq))) {
> hdr = buf_msg(skb);
> --
> 2.17.1
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