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

[pespin]

pespin has uploaded this change for review. ( 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 later has later on priority 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, 3 insertions(+), 1 deletion(-)



  git pull ssh://gerrit.osmocom.org:29418/osmo-pcu refs/changes/36/22436/1

diff --git a/src/gprs_rlcmac_sched.cpp b/src/gprs_rlcmac_sched.cpp
index 49a8ff2..8404456 100644
--- a/src/gprs_rlcmac_sched.cpp
+++ b/src/gprs_rlcmac_sched.cpp
@@ -282,6 +282,7 @@
 	struct msgb *msg = NULL;
 	struct gprs_rlcmac_dl_tbf *tbf, *prio_tbf = NULL;
 	enum tbf_dl_prio prio, max_prio = DL_PRIO_NONE;
+	const gprs_rlc_dl_window *w;
 
 	uint8_t i, tfi, prio_tfi;
 	int age;
@@ -319,8 +320,9 @@
 		/* 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. */
+		w = static_cast<gprs_rlc_dl_window *>(tbf->window());
 		if (req_mcs_kind == EGPRS_GMSK && tbf->is_egprs_enabled() &&
-		    (prio !=DL_PRIO_CONTROL && prio != DL_PRIO_NEW_DATA)) {
+		    (prio !=DL_PRIO_CONTROL && !(prio == DL_PRIO_NEW_DATA && w->resend_needed() < 0))) {
 			LOGP(DRLCMACSCHED, LOGL_DEBUG, "Cannot downgrade EGPRS TBF with prio %d\n", prio);
 			continue;
 		}

-- 
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Gerrit-Project: osmo-pcu
Gerrit-Branch: master
Gerrit-Change-Id: I253de8e1a190a9adb56160f38892c9e43e2c0272
Gerrit-Change-Number: 22436
Gerrit-PatchSet: 1
Gerrit-Owner: pespin <pespin at sysmocom.de>
Gerrit-MessageType: newchange
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