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net: tcp: Implement persistent timer for sending ZWP

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Instead of sending ZWP from send context, when it is detected that
window is full due to zero-window, implement a proper persistent timer,
that is scheduled once zero-window is detected. The timer is responsible
for sending ZWP to the peer and is canceled once non-zero-window is
notified by the peer.

Additionally, in case peer reported zero-window, do not trigger
retransmission from net_tcp_queue_data(), as it won't be transmitted
anyway by the stack.

Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>
This commit is contained in:
Robert Lubos 2022-05-10 15:13:21 +02:00 • committed by Carles Cufí
commit d35d9a6158
2 changed files with 35 additions and 3 deletions
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36
subsys/net/ip/tcp.c
View file

@ -426,8 +426,9 @@ static int tcp_conn_unref(struct tcp *conn, int status)
tcp_pkt_unref(conn->queue_recv_data);
}
k_work_cancel_delayable(&conn->timewait_timer);
k_work_cancel_delayable(&conn->fin_timer);
(void)k_work_cancel_delayable(&conn->timewait_timer);
(void)k_work_cancel_delayable(&conn->fin_timer);
(void)k_work_cancel_delayable(&conn->persist_timer);
sys_slist_find_and_remove(&tcp_conns, &conn->next);
@ -1224,6 +1225,23 @@ static void tcp_fin_timeout(struct k_work *work)
net_context_unref(conn->context);
}
static void tcp_send_zwp(struct k_work *work)
{
struct k_work_delayable *dwork = k_work_delayable_from_work(work);
struct tcp *conn = CONTAINER_OF(dwork, struct tcp, persist_timer);
k_mutex_lock(&conn->lock, K_FOREVER);
(void)tcp_out_ext(conn, ACK, NULL, conn->seq - 1);
if (conn->send_win == 0) {
(void)k_work_reschedule_for_queue(
&tcp_work_q, &conn->persist_timer, K_MSEC(tcp_rto));
}
k_mutex_unlock(&conn->lock);
}
static void tcp_conn_ref(struct tcp *conn)
{
int ref_count = atomic_inc(&conn->ref_count) + 1;
@ -1290,6 +1308,7 @@ static struct tcp *tcp_conn_alloc(struct net_context *context)
k_work_init_delayable(&conn->fin_timer, tcp_fin_timeout);
k_work_init_delayable(&conn->send_data_timer, tcp_resend_data);
k_work_init_delayable(&conn->recv_queue_timer, tcp_cleanup_recv_queue);
k_work_init_delayable(&conn->persist_timer, tcp_send_zwp);
tcp_conn_ref(conn);
@ -1835,6 +1854,13 @@ static void tcp_in(struct tcp *conn, struct net_pkt *pkt)
conn->send_win = max_win;
}
if (conn->send_win == 0) {
(void)k_work_reschedule_for_queue(
&tcp_work_q, &conn->persist_timer, K_MSEC(tcp_rto));
} else {
(void)k_work_cancel_delayable(&conn->persist_timer);
}
if (tcp_window_full(conn)) {
(void)k_sem_take(&conn->tx_sem, K_NO_WAIT);
} else {
@ -2256,7 +2282,11 @@ int net_tcp_queue_data(struct net_context *context, struct net_pkt *pkt)
if (tcp_window_full(conn)) {
if (conn->send_win == 0) {
tcp_out_ext(conn, ACK, NULL, conn->seq - 1);
/* No point retransmiting if the current TX window size
* is 0.
*/
ret = -EAGAIN;
goto out;
}
/* Trigger resend if the timer is not active */

2
subsys/net/ip/tcp_private.h
View file

@ -242,6 +242,8 @@ struct tcp { /* TCP connection */
struct k_work_delayable recv_queue_timer;
struct k_work_delayable send_data_timer;
struct k_work_delayable timewait_timer;
struct k_work_delayable persist_timer;
union {
/* Because FIN and establish timers are never happening
* at the same time, share the timer between them to