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bscc_sccp: Small optimiztion in bsc_sccp_inst_next_conn_id() 

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
This commit is contained in:
Pau Espin 2023-03-09 14:06:21 +01:00
parent 8958269ea9
commit 53cd4ad5fc
1 changed files with 31 additions and 13 deletions
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44
src/osmo-bsc/bsc_sccp.c
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@ -47,6 +47,33 @@ uint32_t bsc_sccp_inst_next_conn_id(struct osmo_sccp_instance *sccp)
/* This looks really suboptimal, but in most cases the static next_id should indicate exactly the next unused
* conn_id, and we only iterate all conns once to make super sure that it is not already in use. */
/* SCCP towards SMLC: */
if (bsc_gsmnet->smlc->sccp == sccp) {
for (i = 0; i < SCCP_CONN_ID_MAX; i++) {
struct gsm_subscriber_connection *conn;
uint32_t conn_id = next_id;
bool conn_id_already_used = false;
/* Optimized modulo operation (% SCCP_CONN_ID_MAX) using bitwise AND plus CMP: */
next_id = (next_id + 1) & 0x00FFFFFF;
if (OSMO_UNLIKELY(next_id == 0x00FFFFFF))
next_id = 0;
llist_for_each_entry(conn, &bsc_gsmnet->subscr_conns, entry) {
if (conn->lcs.lb.state != SUBSCR_SCCP_ST_NONE &&
conn->lcs.lb.conn_id == conn_id) {
conn_id_already_used = true;
break;
}
}
if (!conn_id_already_used)
return conn_id;
}
return 0xFFFFFFFF;
}
/* SCCP towards MSC: */
for (i = 0; i < SCCP_CONN_ID_MAX; i++) {
struct gsm_subscriber_connection *conn;
uint32_t conn_id = next_id;
@ -58,19 +85,10 @@ uint32_t bsc_sccp_inst_next_conn_id(struct osmo_sccp_instance *sccp)
next_id = 0;
llist_for_each_entry(conn, &bsc_gsmnet->subscr_conns, entry) {
if (conn->sccp.msc && conn->sccp.msc->a.sccp == sccp) {
if (conn_id == conn->sccp.conn_id) {
conn_id_already_used = true;
break;
}
}
if (bsc_gsmnet->smlc->sccp == sccp
&& conn->lcs.lb.state != SUBSCR_SCCP_ST_NONE) {
if (conn_id == conn->lcs.lb.conn_id) {
conn_id_already_used = true;
break;
}
if (conn->sccp.msc && conn->sccp.msc->a.sccp == sccp &&
conn->sccp.conn_id == conn_id) {
conn_id_already_used = true;
break;
}
}