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| author | Michael Brown | 2012-07-08 17:51:21 +0200 |
|---|---|---|
| committer | Michael Brown | 2012-07-09 11:13:47 +0200 |
| commit | a5d16a91af4219d4166cf238ff5b9a99c0db4d70 (patch) | |
| tree | 56712799a819006f7cf8dbb1e770710752f5e0b5 /src/net/tcp.c | |
| parent | [arp] Try to avoid discarding ARP cache entries (diff) | |
| download | ipxe-a5d16a91af4219d4166cf238ff5b9a99c0db4d70.tar.gz ipxe-a5d16a91af4219d4166cf238ff5b9a99c0db4d70.tar.xz ipxe-a5d16a91af4219d4166cf238ff5b9a99c0db4d70.zip | |
[tcp] Truncate TCP window to prevent future packet discards
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>
Diffstat (limited to 'src/net/tcp.c')
| -rw-r--r-- | src/net/tcp.c | 23 |
1 files changed, 20 insertions, 3 deletions
diff --git a/src/net/tcp.c b/src/net/tcp.c index e98d8b17..938edd57 100644 --- a/src/net/tcp.c +++ b/src/net/tcp.c @@ -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; } |