diff options
Diffstat (limited to 'tcp.c')
| -rw-r--r-- | tcp.c | 45 |
1 files changed, 33 insertions, 12 deletions
@@ -353,6 +353,9 @@ enum { #define LOW_RTT_TABLE_SIZE 8 #define LOW_RTT_THRESHOLD 10 /* us */ +/* Ratio of buffer to bandwidth * delay product implying interactive traffic */ +#define SNDBUF_TO_BW_DELAY_INTERACTIVE /* > */ 20 /* (i.e. < 5% of buffer) */ + #define ACK_IF_NEEDED 0 /* See tcp_send_flag() */ #define CONN_IS_CLOSING(conn) \ @@ -426,11 +429,13 @@ socklen_t tcp_info_size; sizeof(((struct tcp_info_linux *)NULL)->tcpi_##f_)) <= tcp_info_size) /* Kernel reports sending window in TCP_INFO (kernel commit 8f7baad7f035) */ -#define snd_wnd_cap tcp_info_cap(snd_wnd) +#define snd_wnd_cap tcp_info_cap(snd_wnd) /* Kernel reports bytes acked in TCP_INFO (kernel commit 0df48c26d84) */ -#define bytes_acked_cap tcp_info_cap(bytes_acked) +#define bytes_acked_cap tcp_info_cap(bytes_acked) /* Kernel reports minimum RTT in TCP_INFO (kernel commit cd9b266095f4) */ -#define min_rtt_cap tcp_info_cap(min_rtt) +#define min_rtt_cap tcp_info_cap(min_rtt) +/* Kernel reports delivery rate in TCP_INFO (kernel commit eb8329e0a04d) */ +#define delivery_rate_cap tcp_info_cap(delivery_rate) /* sendmsg() to socket */ static struct iovec tcp_iov [UIO_MAXIOV]; @@ -1051,6 +1056,7 @@ int tcp_update_seqack_wnd(const struct ctx *c, struct tcp_tap_conn *conn, socklen_t sl = sizeof(*tinfo); struct tcp_info_linux tinfo_new; uint32_t new_wnd_to_tap = prev_wnd_to_tap; + bool ack_everything = true; int s = conn->sock; /* At this point we could ack all the data we've accepted for forwarding @@ -1060,7 +1066,8 @@ int tcp_update_seqack_wnd(const struct ctx *c, struct tcp_tap_conn *conn, * control behaviour. * * For it to be possible and worth it we need: - * - The TCP_INFO Linux extension which gives us the peer acked bytes + * - The TCP_INFO Linux extensions which give us the peer acked bytes + * and the delivery rate (outbound bandwidth at receiver) * - Not to be told not to (force_seq) * - Not half-closed in the peer->guest direction * With no data coming from the peer, we might not get events which @@ -1070,19 +1077,36 @@ int tcp_update_seqack_wnd(const struct ctx *c, struct tcp_tap_conn *conn, * Data goes from socket to socket, with nothing meaningfully "in * flight". * - Not a pseudo-local connection (e.g. to a VM on the same host) - * - Large enough send buffer - * In these cases, there's not enough in flight to bother. + * If it is, there's not enough in flight to bother. + * - Sending buffer significantly larger than bandwidth * delay product + * Meaning we're not bandwidth-bound and this is likely to be + * interactive traffic where we want to preserve transparent + * connection behaviour and latency. + * + * Otherwise, we probably want to maximise throughput, which needs + * sending buffer auto-tuning, triggered in turn by filling up the + * outbound socket queue. */ - if (bytes_acked_cap && !force_seq && + if (bytes_acked_cap && delivery_rate_cap && !force_seq && !CONN_IS_CLOSING(conn) && - !(conn->flags & LOCAL) && !tcp_rtt_dst_low(conn) && - (unsigned)SNDBUF_GET(conn) >= SNDBUF_SMALL) { + !(conn->flags & LOCAL) && !tcp_rtt_dst_low(conn)) { if (!tinfo) { tinfo = &tinfo_new; if (getsockopt(s, SOL_TCP, TCP_INFO, tinfo, &sl)) return 0; } + if ((unsigned)SNDBUF_GET(conn) > (long long)tinfo->tcpi_rtt * + tinfo->tcpi_delivery_rate / + 1000 / 1000 * + SNDBUF_TO_BW_DELAY_INTERACTIVE) + ack_everything = false; + } + + if (ack_everything) { + /* Fall back to acknowledging everything we got */ + conn->seq_ack_to_tap = conn->seq_from_tap; + } else { /* This trips a cppcheck bug in some versions, including * cppcheck 2.18.3. * https://sourceforge.net/p/cppcheck/discussion/general/thread/fecde59085/ @@ -1090,9 +1114,6 @@ int tcp_update_seqack_wnd(const struct ctx *c, struct tcp_tap_conn *conn, /* cppcheck-suppress [uninitvar,unmatchedSuppression] */ conn->seq_ack_to_tap = tinfo->tcpi_bytes_acked + conn->seq_init_from_tap; - } else { - /* Fall back to acknowledging everything we got */ - conn->seq_ack_to_tap = conn->seq_from_tap; } /* It's occasionally possible for us to go from using the fallback above |