Change in osmo-pcu[master]: sched: Avoid picking TBF with nacked dl blocks when GMSK is required

[pespin]

pespin has submitted this change. ( https://gerrit.osmocom.org/c/osmo-pcu/+/22436 )

Change subject: sched: Avoid picking TBF with nacked dl blocks when GMSK is required
......................................................................

sched: Avoid picking TBF with nacked dl blocks when GMSK is required

Sine we don't yet implement properly all resegmentation of blocks from
same MCS family type, when requiring a GMSK DL block (due to GPRS+EGPRS
multiplexing limitations) we need to skip retransmitions, otherwise we'd
be incorrectly picking a DL block which was already built with a
potentially higher MCS value.

The "DL_PRIO_NEW_DATA" prio serves two purposes:
* There's new data to send
* There's some nacked data to be retransmitted

The 2nd purpose has, later on, more priority over the 1st one when the tbf
is selected (see gprs_rlcmac_dl_tbf::take_next_bsn()).

Until now we were handling correctly the case where the tbf was skipped
in case the prio was to resend unacked data (DL_PRIO_SENT_DATA), but
was incorrectly selected when it'd send nacked data. Let's fix it by
specifically checking w->resend_needed() < 0.

Change-Id: I253de8e1a190a9adb56160f38892c9e43e2c0272
---
M src/gprs_rlcmac_sched.cpp
1 file changed, 28 insertions(+), 3 deletions(-)

Approvals:
  pespin: Looks good to me, approved
  Jenkins Builder: Verified



diff --git a/src/gprs_rlcmac_sched.cpp b/src/gprs_rlcmac_sched.cpp
index 49a8ff2..6dea949 100644
--- a/src/gprs_rlcmac_sched.cpp
+++ b/src/gprs_rlcmac_sched.cpp
@@ -275,6 +275,31 @@
 	return DL_PRIO_NONE;
 }
 
+/* Check if next data block of a TBF can be encoded in GMSK [(M)CS1-4]. */
+static bool can_produce_gmsk_data_block_next(struct gprs_rlcmac_dl_tbf *tbf, enum tbf_dl_prio prio)
+{
+	const gprs_rlc_dl_window *w;
+
+	/* GPRS TBFs can always send GMSK */
+	if (!tbf->is_egprs_enabled())
+		return true;
+
+	switch (prio) {
+	case DL_PRIO_CONTROL:
+		/* Control blocks are always CS-1 */
+		return true;
+	case DL_PRIO_NEW_DATA:
+		/* We can send any new data (no block generated yet) using any
+		 * MCS. However, we don't (yet) support resegmenting already
+		 * sent blocks (NACKed blocks in this case) into lower MCS of
+		 * the same family. See OS#4966 */
+		w = static_cast<gprs_rlc_dl_window *>(tbf->window());
+		return w->resend_needed() < 0;
+	default:
+		return false;
+	}
+}
+
 static struct msgb *sched_select_downlink(struct gprs_rlcmac_bts *bts,
 		    uint8_t trx, uint8_t ts, uint32_t fn,
 		    uint8_t block_nr, struct gprs_rlcmac_pdch *pdch, enum mcs_kind req_mcs_kind, bool *is_egprs)
@@ -319,9 +344,9 @@
 		/* If a GPRS (CS1-4/MCS1-4) Dl block is required, downgrade MCS
 		 * below instead of skipping. However, downgrade can only be
 		 * done on new data BSNs (not yet sent) and control blocks. */
-		if (req_mcs_kind == EGPRS_GMSK && tbf->is_egprs_enabled() &&
-		    (prio !=DL_PRIO_CONTROL && prio != DL_PRIO_NEW_DATA)) {
-			LOGP(DRLCMACSCHED, LOGL_DEBUG, "Cannot downgrade EGPRS TBF with prio %d\n", prio);
+		if (req_mcs_kind == EGPRS_GMSK && !can_produce_gmsk_data_block_next(tbf, prio)) {
+			LOGP(DRLCMACSCHED, LOGL_DEBUG, "%s Cannot downgrade EGPRS TBF with prio %d\n",
+			     tbf_name(tbf), prio);
 			continue;
 		}
 

-- 
To view, visit https://gerrit.osmocom.org/c/osmo-pcu/+/22436
To unsubscribe, or for help writing mail filters, visit https://gerrit.osmocom.org/settings

Gerrit-Project: osmo-pcu
Gerrit-Branch: master
Gerrit-Change-Id: I253de8e1a190a9adb56160f38892c9e43e2c0272
Gerrit-Change-Number: 22436
Gerrit-PatchSet: 3
Gerrit-Owner: pespin <pespin at sysmocom.de>
Gerrit-Reviewer: Jenkins Builder
Gerrit-Reviewer: laforge <laforge at osmocom.org>
Gerrit-Reviewer: osmith <osmith at sysmocom.de>
Gerrit-Reviewer: pespin <pespin at sysmocom.de>
Gerrit-MessageType: merged
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osmocom.org/pipermail/gerrit-log/attachments/20210126/3c5c9e69/attachment.htm>