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srsLTE
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rlc_am_lte: reduce time holding Tx mutex when processing status PDUs 

the patch is a re-implementation of the customer-specific optimization
we did in order to reduce the time the RLC holds the Tx mutex when
processing an incoming status PDU.

The patch makes sure to never operate on a raw mutex but instead
uses the deadlock-avoiding RAII lock.
This commit is contained in:
Andre Puschmann 2021-06-15 11:59:39 +02:00
parent 9c60ef092c
commit 83bf5dcd49
1 changed files with 46 additions and 37 deletions
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83
lib/src/upper/rlc_am_lte.cc
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@ -1168,48 +1168,55 @@ void rlc_am_lte::rlc_am_lte_tx::handle_control_pdu(uint8_t* payload, uint32_t no
return; return;
} }
std::unique_lock<std::mutex> lock(mutex); // Local variables for handling Status PDU will be updated with lock
rlc_status_pdu_t status = {};
uint32_t i = 0;
uint32_t vt_s_local = 0;
logger.debug(payload, nof_bytes, "%s Rx control PDU", RB_NAME); {
std::lock_guard<std::mutex> lock(mutex);
rlc_status_pdu_t status; logger.debug(payload, nof_bytes, "%s Rx control PDU", RB_NAME);
rlc_am_read_status_pdu(payload, nof_bytes, &status);
log_rlc_am_status_pdu_to_string(logger.info, "%s Rx Status PDU: %s", &status, RB_NAME); rlc_am_read_status_pdu(payload, nof_bytes, &status);
// make sure ACK_SN is within our Tx window log_rlc_am_status_pdu_to_string(logger.info, "%s Rx Status PDU: %s", &status, RB_NAME);
if (((MOD + status.ack_sn - vt_a) % MOD > RLC_AM_WINDOW_SIZE) ||
((MOD + vt_s - status.ack_sn) % MOD > RLC_AM_WINDOW_SIZE)) { // make sure ACK_SN is within our Tx window
logger.warning("%s Received invalid status PDU (ack_sn=%d, vt_a=%d, vt_s=%d). Dropping PDU.", if (((MOD + status.ack_sn - vt_a) % MOD > RLC_AM_WINDOW_SIZE) ||
RB_NAME, ((MOD + vt_s - status.ack_sn) % MOD > RLC_AM_WINDOW_SIZE)) {
status.ack_sn, logger.warning("%s Received invalid status PDU (ack_sn=%d, vt_a=%d, vt_s=%d). Dropping PDU.",
vt_a, RB_NAME,
vt_s); status.ack_sn,
return; vt_a,
vt_s);
return;
}
// Sec 5.2.2.2, stop poll reTx timer if status PDU comprises a positive _or_ negative acknowledgement
// for the RLC data PDU with sequence number poll_sn
if (poll_retx_timer.is_valid() && (TX_MOD_BASE(poll_sn) < TX_MOD_BASE(status.ack_sn))) {
logger.debug("%s Stopping pollRetx timer", RB_NAME);
poll_retx_timer.stop();
}
// flush retx queue to avoid unordered SNs, we expect the Rx to request lost PDUs again
if (status.N_nack > 0) {
retx_queue.clear();
}
i = vt_a;
vt_s_local = vt_s;
} }
// Sec 5.2.2.2, stop poll reTx timer if status PDU comprises a positive _or_ negative acknowledgement bool update_vt_a = true;
// for the RLC data PDU with sequence number poll_sn while (TX_MOD_BASE(i) < TX_MOD_BASE(status.ack_sn) && TX_MOD_BASE(i) < TX_MOD_BASE(vt_s_local)) {
if (poll_retx_timer.is_valid() && (TX_MOD_BASE(poll_sn) < TX_MOD_BASE(status.ack_sn))) {
logger.debug("%s Stopping pollRetx timer", RB_NAME);
poll_retx_timer.stop();
}
// flush retx queue to avoid unordered SNs, we expect the Rx to request lost PDUs again
if (status.N_nack > 0) {
retx_queue.clear();
}
// Handle ACKs and NACKs
bool update_vt_a = true;
uint32_t i = vt_a;
while (TX_MOD_BASE(i) < TX_MOD_BASE(status.ack_sn) && TX_MOD_BASE(i) < TX_MOD_BASE(vt_s)) {
bool nack = false; bool nack = false;
for (uint32_t j = 0; j < status.N_nack; j++) { for (uint32_t j = 0; j < status.N_nack; j++) {
if (status.nacks[j].nack_sn == i) { if (status.nacks[j].nack_sn == i) {
nack = true; nack = true;
update_vt_a = false; update_vt_a = false;
std::lock_guard<std::mutex> lock(mutex);
if (tx_window.has_sn(i)) { if (tx_window.has_sn(i)) {
auto& pdu = tx_window[i]; auto& pdu = tx_window[i];
if (not retx_queue.has_sn(i)) { if (not retx_queue.has_sn(i)) {
@ -1259,6 +1266,7 @@ void rlc_am_lte::rlc_am_lte_tx::handle_control_pdu(uint8_t* payload, uint32_t no
if (!nack) { if (!nack) {
// ACKed SNs get marked and removed from tx_window so PDCP get's only notified once // ACKed SNs get marked and removed from tx_window so PDCP get's only notified once
std::lock_guard<std::mutex> lock(mutex);
if (tx_window.has_sn(i)) { if (tx_window.has_sn(i)) {
update_notification_ack_info(i); update_notification_ack_info(i);
logger.debug("Tx PDU SN=%zd being removed from tx window", i); logger.debug("Tx PDU SN=%zd being removed from tx window", i);
@ -1273,16 +1281,17 @@ void rlc_am_lte::rlc_am_lte_tx::handle_control_pdu(uint8_t* payload, uint32_t no
i = (i + 1) % MOD; i = (i + 1) % MOD;
} }
// Make sure vt_a points to valid SN {
if (not tx_window.empty() && not tx_window.has_sn(vt_a)) { // Make sure vt_a points to valid SN
logger.error("%s vt_a=%d points to invalid position in Tx window.", RB_NAME, vt_a); std::lock_guard<std::mutex> lock(mutex);
parent->rrc->protocol_failure(); if (not tx_window.empty() && not tx_window.has_sn(vt_a)) {
logger.error("%s vt_a=%d points to invalid position in Tx window.", RB_NAME, vt_a);
parent->rrc->protocol_failure();
}
} }
debug_state(); debug_state();
lock.unlock();
// Notify PDCP without holding Tx mutex // Notify PDCP without holding Tx mutex
if (not notify_info_vec.empty()) { if (not notify_info_vec.empty()) {
parent->pdcp->notify_delivery(parent->lcid, notify_info_vec); parent->pdcp->notify_delivery(parent->lcid, notify_info_vec);