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[tcp] Truncate TCP window to prevent future packet discards

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Whenever memory pressure causes a queued packet to be discarded (and
so retransmitted), reduce the maximum TCP window to a size that would
have prevented the discard.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown 2012-07-08 16:51:21 +01:00
parent 024247317d
commit a5d16a91af
1 changed files with 20 additions and 3 deletions
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23
src/net/tcp.c
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@ -97,6 +97,8 @@ struct tcp_connection {
* Equivalent to Rcv.Wind.Scale in RFC 1323 terminology
*/
uint8_t rcv_win_scale;
/** Maximum receive window */
uint32_t max_rcv_win;
/** Transmit queue */
struct list_head tx_queue;
@ -295,6 +297,7 @@ static int tcp_open ( struct interface *xfer, struct sockaddr *peer,
tcp->tcp_state = TCP_STATE_SENT ( TCP_SYN );
tcp_dump_state ( tcp );
tcp->snd_seq = random();
tcp->max_rcv_win = TCP_MAX_WINDOW_SIZE;
INIT_LIST_HEAD ( &tcp->tx_queue );
INIT_LIST_HEAD ( &tcp->rx_queue );
memcpy ( &tcp->peer, st_peer, sizeof ( tcp->peer ) );
@ -557,9 +560,7 @@ static int tcp_xmit ( struct tcp_connection *tcp ) {
tcp_process_tx_queue ( tcp, len, iobuf, 0 );
/* Expand receive window if possible */
max_rcv_win = ( ( freemem * 3 ) / 4 );
if ( max_rcv_win > TCP_MAX_WINDOW_SIZE )
max_rcv_win = TCP_MAX_WINDOW_SIZE;
max_rcv_win = tcp->max_rcv_win;
app_win = xfer_window ( &tcp->xfer );
if ( max_rcv_win > app_win )
max_rcv_win = app_win;
@ -1299,13 +1300,29 @@ struct tcpip_protocol tcp_protocol __tcpip_protocol = {
static unsigned int tcp_discard ( void ) {
struct tcp_connection *tcp;
struct io_buffer *iobuf;
struct tcp_rx_queued_header *tcpqhdr;
uint32_t max_win;
unsigned int discarded = 0;
/* Try to drop one queued RX packet from each connection */
list_for_each_entry ( tcp, &tcp_conns, list ) {
list_for_each_entry_reverse ( iobuf, &tcp->rx_queue, list ) {
/* Limit window to prevent future discards */
tcpqhdr = iobuf->data;
max_win = ( tcpqhdr->seq - tcp->rcv_ack );
if ( max_win < tcp->max_rcv_win ) {
DBGC ( tcp, "TCP %p reducing maximum window "
"from %d to %d\n",
tcp, tcp->max_rcv_win, max_win );
tcp->max_rcv_win = max_win;
}
/* Remove packet from queue */
list_del ( &iobuf->list );
free_iob ( iobuf );
/* Report discard */
discarded++;
break;
}