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由 Yuchung Cheng 提交于
PRR slow start is often too aggressive especially when drops are caused by traffic policers. The policers mainly use token bucket to enforce the rate so sending (twice) faster than the delivery rate causes excessive drops. This patch changes PRR to the conservative reduction bound (CRB) mode in RFC 6937 by default. CRB follows the packet conservation rule to send at most the delivery rate by default. But if many packets are lost and the pipe is empty, CRB may take N round trips to repair N losses. We conditionally turn on slow start mode if all these conditions are made to speed up the recovery: 1) on the second round or later in recovery 2) retransmission sent in the previous round is delivered on this ACK 3) no retransmission is marked lost on this ACK By using packet conservation by default, this change reduces the loss retransmits signicantly on networks that deploy traffic policers, up to 20% reduction of overall loss rate. Signed-off-by: NYuchung Cheng <ycheng@google.com> Signed-off-by: NNandita Dukkipati <nanditad@google.com> Signed-off-by: NNeal Cardwell <ncardwell@google.com> Signed-off-by: NDavid S. Miller <davem@davemloft.net>
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