In osmo-bsc, there's currently 0..1 Lb links and 0..N A links, where N
is the number of MSC, but links can be shared in the underlaying stack
(struct osmo_sccp_instance), hence range 0..N of different
osmo_sccp_instance (identified by PC).
Even more, the Lb and A link can share the same underlaying stack, so
osmo-bsc can end up with only 1 struct osmo_sccp_instance shared by all
the above mentioned links in case all are configured under the same PC.
Total range A+Lb is 0..(1+N).
A struct gsm_subscriber_conn stores 2 struct sccp_instance*, one for
Lb (conn->lcs.lb.*)and one for A (conn->sccp.*).
They can actually point to the same sccp_instance or to different ones,
as explained above, depending on the configured setup. In any case, a
gsm_subscriber_conn needs 2 rb_nodes since it can hold
any of the 2 conn_ids independently (A or Lb).
The previous patch forgot to add that 2nd rb_node as well as some
initialization and release code for the Lb conn. This patch addresses
that.
When the 2nd rb_node, a problem when iterating the rbtree appears: how to
find out the "conn" pointer from the rb_node pointer, since the rb_node pointer
can be any of the 2 rb_nodes inside the struct at a different offsets.
In order to solve that problem, a new struct bscp_sccp_conn_node is
added, which holds all the relevant information used by the rbtree lookup code
in a generic way (rb_node and conn_id), plus a backpointer to the struct
bsc_gsm_subcriber it relates too.
Fixes: 85062ccad3
Change-Id: If42d93adee71d646766929a09bc01ae92b734ef3
It was found that, on a busy osmo-bsc (>1000 concurrent calls spread over
several BTS), the CPU consumption looking up for gsm_subscriber_conn
based on SCCP conn_id can take a considerable amount of time (>5% of
osmo-bsc already taking 70% of the CPU time on the core it is running on).
The huge CPU consumption happens because a linear search is done (llist)
over the entire list of SCCP connections every time an SCCP message is
handled.
In order to optimize this lookup, this patch introduces a new struct
bsc_sccp_inst which becomes associated to the libosmo-sccp
osmo_sccp_instance. Each of this strucs maintains an rbtree of
gsm_subscriber_conn ordered by conn_id.
As a result algorithmic complexity adds O(log(N)) during insert, lookup
and delete of SCCP conns, but gets rid of O(N) previous lookup.
As a plus, finding a new conn_id now takes generally O(log(N)), while
before it used to take O(N).
Related: SYS#6200
Change-Id: I667d3ec1dad0ab7bc0fa4799d9611f3a914d07e5
Refactor the double loop to check a code path matching the sccp_instance
once instead of doing so for every subscr_conn.
If for instance let's say we have 1000 concurrent calls in progress,
which means we have 1000 subscr_conn, which means we at least do the
extra check regarding SMLC vs MSC 1000 times (at least, xN times if N
conn_id already used are already found).
That overhead happens every time a new subscr_conn is created (which in
a BSC with already 1000 concurrent calls can potentially happen quite
frequently).
Change-Id: Ic32b1eeb201fc51110e1ee130110824845f81e82
The 0x00FFFFFF source local reference is reserved in M3UA/SCCP, hence
avoid allocating a conn_id with that value since later on when reused as
a source local reference it would fail to be encoded.
Change-Id: I5c62bbfa89140d754edccb4404503cb70d5fde89
Currently, the conn_id is allocated in a range 0..0xffffff by
bsc_sccp_inst_next_conn_id(), and -1 means it is unset.
This means allocation expects "int" to be at least 32 bits integer,
in order to fit 24 bits for 0..0xffffff plus the -1.
Hence, let's define the variable as uint32_t, as already done in
libosmo-sccp. Use last value 0xFFFFFFFF ((uint32_t)-1) and avoid playing
with the value being unsigned sometimes and signed only for "unset"
value.
The value is actually already handled as unsigned (printed with %u) in
most places.
Change-Id: If019bcbc1e28929fe8d981fef9103835fc6ead2e
When adding the Lb interface, it is necessary to determine an unused conn id
across *all* SCCP users. Prepare adding Lb by moving conn id creation out of
the gscon code and generalizing.
Change-Id: I12fcb18f6e4380f72929cfe7681bac05330a8c9a
Pau Espin
Neels Hofmeyr