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don't treat loss of MTU probe packet as a congestion signal

This commit is contained in:
arvidn 2019-01-05 17:12:49 +01:00 committed by Arvid Norberg
parent c6128e31c1
commit 0ce899e273
1 changed files with 63 additions and 52 deletions
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115
src/utp_stream.cpp
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@ -1642,20 +1642,21 @@ void utp_socket_impl::parse_sack(boost::uint16_t const packet_ack, boost::uint8_
packet* p = m_outbuf.at(pkt_seq);
UTP_LOGV("%8p: Packet %d lost. (fast_resend_seq_nr:%d trigger fast-resend)\n"
, static_cast<void*>(this), pkt_seq, m_fast_resend_seq_nr);
if (p)
{
if (resend_packet(p, true))
{
m_duplicate_acks = 0;
m_fast_resend_seq_nr = (pkt_seq + 1) & ACK_MASK;
}
}
if (!p) continue;
if (cut_cwnd)
// don't cut cwnd if the packet we lost was the MTU probe
// the logic to handle a lost MTU probe is in resend_packet()
if (cut_cwnd && (pkt_seq != m_mtu_seq || m_mtu_seq == 0))
{
experienced_loss(pkt_seq);
cut_cwnd = false;
}
if (resend_packet(p, true))
{
m_duplicate_acks = 0;
m_fast_resend_seq_nr = (pkt_seq + 1) & ACK_MASK;
}
}
}
@ -3068,7 +3069,9 @@ bool utp_socket_impl::incoming_packet(boost::uint8_t const* buf, int size
if (p)
{
experienced_loss(m_fast_resend_seq_nr);
// don't consider a lost probe as proper loss, it doesn't necessarily
// signal congestion
if (!p->mtu_probe) experienced_loss(m_fast_resend_seq_nr);
resend_packet(p, true);
if (m_state == UTP_STATE_ERROR_WAIT || m_state == UTP_STATE_DELETE) return true;
}
@ -3632,7 +3635,20 @@ void utp_socket_impl::tick(time_point const now)
if (now > m_timeout)
{
// TIMEOUT!
// set cwnd to 1 MSS
bool ignore_loss = false;
if (((m_acked_seq_nr + 1) & ACK_MASK) == m_mtu_seq
&& ((m_seq_nr - 1) & ACK_MASK) == m_mtu_seq
&& m_mtu_seq != 0)
{
// we timed out, and the only outstanding packet
// we had was the probe. Assume it was dropped
// because it was too big
m_mtu_ceiling = m_mtu - 1;
update_mtu_limits();
ignore_loss = true;
}
// the close_reason here is a bit of a hack. When it's set, it indicates
// that the upper layer intends to close the socket. However, it has been
@ -3641,7 +3657,9 @@ void utp_socket_impl::tick(time_point const now)
// other end. This catches that case and let the socket time out.
if (m_outbuf.size() || m_close_reason != 0)
{
++m_num_timeouts;
// m_num_timeouts is used to update the connection timeout, and if we
// lose this packet because it's an MTU-probe, don't change the timeout
if (!ignore_loss) ++m_num_timeouts;
m_sm->inc_stats_counter(counters::utp_timeout);
}
@ -3667,52 +3685,45 @@ void utp_socket_impl::tick(time_point const now)
return;
}
if (((m_acked_seq_nr + 1) & ACK_MASK) == m_mtu_seq
&& ((m_seq_nr - 1) & ACK_MASK) == m_mtu_seq
&& m_mtu_seq != 0)
if (!ignore_loss)
{
// we timed out, and the only outstanding packet
// we had was the probe. Assume it was dropped
// because it was too big
m_mtu_ceiling = m_mtu - 1;
update_mtu_limits();
// set cwnd to 1 MSS
if (m_bytes_in_flight == 0 && (m_cwnd >> 16) >= m_mtu)
{
// this is just a timeout because this direction of
// the stream is idle. Don't reset the cwnd, just decay it
m_cwnd = std::max(m_cwnd * 2 / 3, boost::int64_t(m_mtu) * (1 << 16));
}
else
{
// we timed out because a packet was not ACKed or because
// the cwnd was made smaller than one packet
m_cwnd = boost::int64_t(m_mtu) * (1 << 16);
}
TORRENT_ASSERT(m_cwnd >= 0);
m_timeout = now + milliseconds(packet_timeout());
UTP_LOGV("%8p: resetting cwnd:%d\n"
, static_cast<void*>(this), int(m_cwnd >> 16));
// since we've already timed out now, don't count
// loss that we might detect for packets that just
// timed out
m_loss_seq_nr = m_seq_nr;
// when we time out, the cwnd is reset to 1 MSS, which means we
// need to ramp it up quickly again. enter slow start mode. This time
// we're very likely to have an ssthres set, which will make us leave
// slow start before inducing more delay or loss.
m_slow_start = true;
UTP_LOGV("%8p: slow_start -> 1\n", static_cast<void*>(this));
}
if (m_bytes_in_flight == 0 && (m_cwnd >> 16) >= m_mtu)
{
// this is just a timeout because this direction of
// the stream is idle. Don't reset the cwnd, just decay it
m_cwnd = std::max(m_cwnd * 2 / 3, boost::int64_t(m_mtu) * (1 << 16));
}
else
{
// we timed out because a packet was not ACKed or because
// the cwnd was made smaller than one packet
m_cwnd = boost::int64_t(m_mtu) * (1 << 16);
}
TORRENT_ASSERT(m_cwnd >= 0);
m_timeout = now + milliseconds(packet_timeout());
UTP_LOGV("%8p: resetting cwnd:%d\n"
, static_cast<void*>(this), int(m_cwnd >> 16));
// we dropped all packets, that includes the mtu probe
m_mtu_seq = 0;
// since we've already timed out now, don't count
// loss that we might detect for packets that just
// timed out
m_loss_seq_nr = m_seq_nr;
// when we time out, the cwnd is reset to 1 MSS, which means we
// need to ramp it up quickly again. enter slow start mode. This time
// we're very likely to have an ssthres set, which will make us leave
// slow start before inducing more delay or loss.
m_slow_start = true;
UTP_LOGV("%8p: slow_start -> 1\n", static_cast<void*>(this));
// we need to go one past m_seq_nr to cover the case
// where we just sent a SYN packet and then adjusted for
// the uTorrent sequence number reuse