alloc: Use least reserved PDCH for algo A

Currently the slot selection of algorithm A is based on the current
slot usage by active TBF. Especially in the Dl after UL case which
reflects the commen use case "MS initiates TCP connection", the
resulting distribution is not optimal with respect to PDCH usage.

This commit changes the implementation to use the slot reservation
information instead.

Sponsored-by: On-Waves ehf

1 files changed, 60 insertions, 1 deletions

diff --git a/src/gprs_rlcmac_ts_alloc.cpp b/src/gprs_rlcmac_ts_alloc.cpp
index 8c42bb19..c1b73398 100644
--- a/src/gprs_rlcmac_ts_alloc.cpp
+++ b/src/gprs_rlcmac_ts_alloc.cpp
@@ -234,6 +234,65 @@ static int find_least_busy_pdch(struct gprs_rlcmac_trx *trx,
 	return min_ts;
 }
 
+static int find_least_reserved_pdch(struct gprs_rlcmac_trx *trx,
+	enum gprs_rlcmac_tbf_direction dir,
+	uint8_t mask,
+	int *free_usf = 0)
+{
+	unsigned ts;
+	int min_used = INT_MAX;
+	int min_ts = -1;
+	int min_usf = -1;
+
+	for (ts = 0; ts < ARRAY_SIZE(trx->pdch); ts++) {
+		struct gprs_rlcmac_pdch *pdch = &trx->pdch[ts];
+		int num_tbfs;
+		int usf = -1; /* must be signed */
+
+		if (((1 << ts) & mask) == 0)
+			continue;
+
+		num_tbfs =
+			pdch->num_reserved(GPRS_RLCMAC_DL_TBF) +
+			pdch->num_reserved(GPRS_RLCMAC_UL_TBF);
+
+		if (num_tbfs < min_used) {
+			/* We have found a candidate */
+			/* Make sure that an USF is available */
+			if (dir == GPRS_RLCMAC_UL_TBF) {
+				usf = find_free_usf(pdch);
+				if (usf < 0) {
+					LOGP(DRLCMAC, LOGL_DEBUG,
+						"- Skipping TS %d, because "
+						"no USF available\n", ts);
+					continue;
+				}
+			}
+			if (min_ts >= 0)
+				LOGP(DRLCMAC, LOGL_DEBUG,
+					"- Skipping TS %d, because "
+					"num TBFs %d > %d\n",
+					min_ts, min_used, num_tbfs);
+			min_used = num_tbfs;
+			min_ts = ts;
+			min_usf = usf;
+		} else {
+			LOGP(DRLCMAC, LOGL_DEBUG,
+				"- Skipping TS %d, because "
+				"num TBFs %d >= %d\n",
+				ts, num_tbfs, min_used);
+		}
+	}
+
+	if (min_ts < 0)
+		return -1;
+
+	if (free_usf)
+		*free_usf = min_usf;
+
+	return min_ts;
+}
+
 static void attach_tbf_to_pdch(struct gprs_rlcmac_pdch *pdch,
 	struct gprs_rlcmac_tbf *tbf)
 {
@@ -297,7 +356,7 @@ int alloc_algorithm_a(struct gprs_rlcmac_bts *bts,
 	if (!mask)
 		return -EINVAL;
 
-	ts = find_least_busy_pdch(tbf->trx, tbf->direction, mask, &usf);
+	ts = find_least_reserved_pdch(tbf->trx, tbf->direction, mask, &usf);
 
 	if (ts < 0) {
 		LOGP(DRLCMAC, LOGL_NOTICE, "- Failed "