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authorYuchung Cheng <ycheng@google.com>2018-05-17 01:40:15 +0200
committerDavid S. Miller <davem@davemloft.net>2018-05-17 21:41:29 +0200
commitc77d62ffae377de331a19020c0b598a6faceb0ef (patch)
tree697a757111937b5ed3162e1b48c7f53580a0cb31 /drivers/accessibility
parenttcp: new helper tcp_timeout_mark_lost (diff)
downloadlinux-c77d62ffae377de331a19020c0b598a6faceb0ef.tar.xz
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tcp: separate loss marking and state update on RTO
Previously when TCP times out, it first updates cwnd and ssthresh, marks packets lost, and then updates congestion state again. This was fine because everything not yet delivered is marked lost, so the inflight is always 0 and cwnd can be safely set to 1 to retransmit one packet on timeout. But the inflight may not always be 0 on timeout if TCP changes to mark packets lost based on packet sent time. Therefore we must first mark the packet lost, then set the cwnd based on the (updated) inflight. This is not a pure refactor. Congestion control may potentially break if it uses (not yet updated) inflight to compute ssthresh. Fortunately all existing congestion control modules does not do that. Also it changes the inflight when CA_LOSS_EVENT is called, and only westwood processes such an event but does not use inflight. This change has two other minor side benefits: 1) consistent with Fast Recovery s.t. the inflight is updated first before tcp_enter_recovery flips state to CA_Recovery. 2) avoid intertwining loss marking with state update, making the code more readable. Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Reviewed-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Soheil Hassas Yeganeh <soheil@google.com> Reviewed-by: Priyaranjan Jha <priyarjha@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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