paging: Take into account extra delay of all paging groups in BSC queue

So far we only calculated the expiration time based on the amount of
requests of the same paging group in the BSC queue.
However, also extra time has to be taken into account regarding requests
of other paging groups. This is important because requests of all paging
groups are mixed in the BSC queue, meaning having a lot of requests from
other groups before a certain req will anyway delay transmit of that
req to some extend.

Related: OS#5537
Change-Id: Ib55f947c5d3490b27e1d08d39392992919512f9a

1 files changed, 30 insertions, 9 deletions

diff --git a/src/osmo-bsc/paging.c b/src/osmo-bsc/paging.c
index 12937397f..90a0d1264 100644
--- a/src/osmo-bsc/paging.c
+++ b/src/osmo-bsc/paging.c
@@ -340,9 +340,11 @@ static void paging_T3113_expired(void *data)
 }
 
 #define GSM51_MFRAME_DURATION_us (51 * GSM_TDMA_FN_DURATION_uS) /* 235365 us */
-static unsigned int paging_estimate_delay_us(struct gsm_bts *bts, unsigned int num_reqs);
+static unsigned int paging_estimate_delay_us(struct gsm_bts *bts, unsigned int num_reqs,
+					     unsigned int num_reqs_same_pgroup);
 
-static unsigned int calculate_timer_3113(struct gsm_paging_request *req, unsigned int reqs_before)
+static unsigned int calculate_timer_3113(struct gsm_paging_request *req, unsigned int reqs_before,
+					 unsigned int reqs_before_same_pgroup)
 {
 	unsigned int to_us, to;
 	struct gsm_bts *bts = req->bts;
@@ -369,7 +371,7 @@ static unsigned int calculate_timer_3113(struct gsm_paging_request *req, unsigne
 		GSM_TDMA_FN_DURATION_uS * rach_tx_integer * rach_max_trans;
 
 	/* Now add some extra time based on how many requests need to be transmitted before this one: */
-	to_us += paging_estimate_delay_us(bts, reqs_before);
+	to_us += paging_estimate_delay_us(bts, reqs_before, reqs_before_same_pgroup);
 
 	/* ceiling in seconds + extra time */
 	to = (to_us + 999999) / 1000000 + d->val;
@@ -388,7 +390,7 @@ static int _paging_request(const struct bsc_paging_params *params, struct gsm_bt
 	struct gsm_bts_paging_state *bts_entry = &bts->paging;
 	struct gsm_paging_request *req, *last_initial_req = NULL;
 	unsigned int t3113_timeout_s;
-	unsigned int reqs_before_same_pgroup = 0;
+	unsigned int reqs_before = 0, reqs_before_same_pgroup = 0;
 	uint8_t pgroup = gsm0502_calc_paging_group(&bts->si_common.chan_desc,
 						   str_to_imsi(params->bsub->imsi));
 
@@ -410,10 +412,12 @@ static int _paging_request(const struct bsc_paging_params *params, struct gsm_bt
 		}
 		if (req->attempts == 0) {
 			last_initial_req = req;
+			reqs_before++;
 			if (req->pgroup == pgroup)
 				reqs_before_same_pgroup++;
 		} else if (last_initial_req == NULL) {
 			/* If no req with attempts=0 was found, we'll append to end of list, so keep counting. */
+			reqs_before++;
 			if (req->pgroup == pgroup)
 				reqs_before_same_pgroup++;
 		}
@@ -438,7 +442,7 @@ static int _paging_request(const struct bsc_paging_params *params, struct gsm_bt
 	else/* Add in the middle of the list after last_initial_req */
 		__llist_add(&req->entry, &last_initial_req->entry, last_initial_req->entry.next);
 
-	t3113_timeout_s = calculate_timer_3113(req, reqs_before_same_pgroup);
+	t3113_timeout_s = calculate_timer_3113(req, reqs_before, reqs_before_same_pgroup);
 	osmo_timer_schedule(&req->T3113, t3113_timeout_s, 0);
 
 	/* Trigger scheduler if needed: */
@@ -648,11 +652,28 @@ uint16_t paging_estimate_available_slots(struct gsm_bts *bts, unsigned int time_
 /*! Conservative estimate of time needed by BTS to schedule a number of paging
  * requests (num_reqs), based on current load at the BSC queue (doesn't take into
  * account BTs own buffer) */
-static unsigned int paging_estimate_delay_us(struct gsm_bts *bts, unsigned int num_reqs)
+static unsigned int paging_estimate_delay_us(struct gsm_bts *bts, unsigned int num_reqs,
+					     unsigned int num_reqs_same_pgroup)
 {
-	unsigned int n_pag_blocks = gsm0502_get_n_pag_blocks(&bts->si_common.chan_desc);
-	unsigned int n_mframes = (num_reqs + (n_pag_blocks - 1)) / n_pag_blocks;
-	unsigned int time_us = n_mframes * GSM51_MFRAME_DURATION_us;
+	unsigned int n_pag_blocks, n_mframes, time_us = 0;
+
+	n_pag_blocks = gsm0502_get_n_pag_blocks(&bts->si_common.chan_desc);
+
+	/* First of all, we need to extend the timeout in relation to the amount
+	 * of paging requests in the BSC queue. In here we don't care about the
+	 * paging group, because they are mixed in the same queue. If we don't
+	 * take this into account, it could happen that if lots of requests are
+	 * received at the BSC (from MSC) around the same time, they could time
+	 * out in the BSC queue before arriving at the BTS. We already account of
+	 * same-paging-group ones further below, so don't take them into account
+	 * here: */
+	unsigned int num_reqs_other_groups = num_reqs - num_reqs_same_pgroup;
+	time_us += ((num_reqs_other_groups * GSM51_MFRAME_DURATION_us) + (n_pag_blocks - 1)) / n_pag_blocks;
+
+	/* Now we extend the timeout based on the amount of requests of the same
+	 * paging group before the present one: */
+	n_mframes = (num_reqs_same_pgroup + (n_pag_blocks - 1)) / n_pag_blocks;
+	time_us += n_mframes * GSM51_MFRAME_DURATION_us;
 	/* the multiframes are not consecutive for a paging group, let's add the spacing between: */
 	if (n_mframes > 1) {
 		unsigned int bs_pa_mfrms = (bts->si_common.chan_desc.bs_pa_mfrms + 2);