tbf: Fix scheduling for DL Ack/Nack request

Currently the DL Ack/Nack is not requested, if the last chunk of the
final LLC frame in the TBF fits exactly into the remaining space of
the RLC block. It is also not requested, if the RRBP flag cannot be
set due to scheduling issues (single block allocation, polling
already pending for this TBF, ...). So up to POLL_ACK_AFTER_FRAMES
(20) RLC data blocks will have to be resent, before requesting the
Ack/Nack will be retried.

This commit removes the first_fin_ack parameter of
create_dl_acked_block entirely and adds a request_dl_ack() method
that should be called, when the TBF's state changes to FINISHED. This
request will be reset, when the block has been scheduled
successfully. Since the first_fin_ack hasn't been set if chunk ==
space, calling request_dl_ack() on both places in create_new_bsn()
when the state is changed to FINISHED will also fix the first issue
described above.

Note that DL scheduling might not be fair concerning access to
first_ts when multiple TS are used for a TBF. In theory, a TBF might
never get access to first_ts in the worst case.

Sponsored-by: On-Waves ehf

1 files changed, 19 insertions, 12 deletions

diff --git a/src/tbf_dl.cpp b/src/tbf_dl.cpp
index 89ca9c2a..dea18bd7 100644
--- a/src/tbf_dl.cpp
+++ b/src/tbf_dl.cpp
@@ -252,7 +252,7 @@ do_resend:
 		/* re-send block with negative aknowlegement */
 		m_window.m_v_b.mark_unacked(resend_bsn);
 		bts->rlc_resent();
-		return create_dl_acked_block(fn, ts, resend_bsn, false);
+		return create_dl_acked_block(fn, ts, resend_bsn);
 	}
 
 	/* if the window has stalled, or transfer is complete,
@@ -281,7 +281,7 @@ do_resend:
 			/* we just send final block again */
 			int16_t index = m_window.v_s_mod(-1);
 			bts->rlc_resent();
-			return create_dl_acked_block(fn, ts, index, false);
+			return create_dl_acked_block(fn, ts, index);
 		}
 		
 		/* cycle through all unacked blocks */
@@ -295,7 +295,7 @@ do_resend:
 				" != V(S). PLEASE FIX!\n");
 			/* we just send final block again */
 			int16_t index = m_window.v_s_mod(-1);
-			return create_dl_acked_block(fn, ts, index, false);
+			return create_dl_acked_block(fn, ts, index);
 		}
 		goto do_resend;
 	}
@@ -311,7 +311,6 @@ struct msgb *gprs_rlcmac_dl_tbf::create_new_bsn(const uint32_t fn, const uint8_t
 	uint8_t *delimiter, *data, *e_pointer;
 	uint16_t space, chunk;
 	gprs_rlc_data *rlc_data;
-	bool first_fin_ack = false;
 	const uint16_t bsn = m_window.v_s();
 
 	LOGP(DRLCMACDL, LOGL_DEBUG, "- Sending new block at BSN %d\n",
@@ -377,6 +376,7 @@ struct msgb *gprs_rlcmac_dl_tbf::create_new_bsn(const uint32_t fn, const uint8_t
 			m_llc.reset();
 			/* final block */
 			rh->fbi = 1; /* we indicate final block */
+			request_dl_ack();
 			set_state(GPRS_RLCMAC_FINISHED);
 			/* return data block as message */
 			break;
@@ -448,8 +448,7 @@ struct msgb *gprs_rlcmac_dl_tbf::create_new_bsn(const uint32_t fn, const uint8_t
 				"done.\n");
 			li->e = 1; /* we cannot extend */
 			rh->fbi = 1; /* we indicate final block */
-			first_fin_ack = true;
-				/* + 1 indicates: first final ack */
+			request_dl_ack();
 			set_state(GPRS_RLCMAC_FINISHED);
 			break;
 		}
@@ -467,12 +466,17 @@ struct msgb *gprs_rlcmac_dl_tbf::create_new_bsn(const uint32_t fn, const uint8_t
 	m_window.m_v_b.mark_unacked(bsn);
 	m_window.increment_send();
 
-	return create_dl_acked_block(fn, ts, bsn, first_fin_ack);
+	return create_dl_acked_block(fn, ts, bsn);
+}
+
+void gprs_rlcmac_dl_tbf::request_dl_ack()
+{
+	m_dl_ack_requested = true;
 }
 
 struct msgb *gprs_rlcmac_dl_tbf::create_dl_acked_block(
 				const uint32_t fn, const uint8_t ts,
-				const int index, const bool first_fin_ack)
+				const int index)
 {
 	uint8_t *data;
 	struct rlc_dl_header *rh;
@@ -491,11 +495,12 @@ struct msgb *gprs_rlcmac_dl_tbf::create_dl_acked_block(
 		
 	/* poll after POLL_ACK_AFTER_FRAMES frames, or when final block is tx.
 	 */
-	if (m_tx_counter >= POLL_ACK_AFTER_FRAMES || first_fin_ack ||
+	if (m_tx_counter >= POLL_ACK_AFTER_FRAMES || m_dl_ack_requested ||
 			need_poll) {
-		if (first_fin_ack) {
+		if (m_dl_ack_requested) {
 			LOGP(DRLCMACDL, LOGL_DEBUG, "- Scheduling Ack/Nack "
-				"polling, because first final block sent.\n");
+				"polling, because is was requested explicitly "
+				"(e.g. first final block sent).\n");
 		} else if (need_poll) {
 			LOGP(DRLCMACDL, LOGL_DEBUG, "- Scheduling Ack/Nack "
 				"polling, because polling timed out.\n");
@@ -513,7 +518,6 @@ struct msgb *gprs_rlcmac_dl_tbf::create_dl_acked_block(
 			LOGP(DRLCMACDL, LOGL_DEBUG, "Polling cannot be "
 				"sheduled in this TS %d, waiting for "
 				"TS %d\n", ts, control_ts);
-#warning "What happens to the first_fin_ack in case something is already scheduled?"
 		else if (bts->sba()->find(trx->trx_no, ts, (fn + 13) % 2715648))
 			LOGP(DRLCMACDL, LOGL_DEBUG, "Polling cannot be "
 				"sheduled, because single block alllocation "
@@ -533,6 +537,9 @@ struct msgb *gprs_rlcmac_dl_tbf::create_dl_acked_block(
 			/* Clear poll timeout flag */
 			state_flags &= ~(1 << GPRS_RLCMAC_FLAG_TO_DL_ACK);
 
+			/* Clear request flag */
+			m_dl_ack_requested = false;
+
 			/* set polling in header */
 			rh->rrbp = 0; /* N+13 */
 			rh->s_p = 1; /* Polling */