gvisor.dev/gvisor@v0.0.0-20240520182842-f9d4d51c7e0f/pkg/tcpip/transport/tcp/reno_recovery.go (about)

     1  // Copyright 2020 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package tcp
    16  
    17  // renoRecovery stores the variables related to TCP Reno loss recovery
    18  // algorithm.
    19  //
    20  // +stateify savable
    21  type renoRecovery struct {
    22  	s *sender
    23  }
    24  
    25  func newRenoRecovery(s *sender) *renoRecovery {
    26  	return &renoRecovery{s: s}
    27  }
    28  
    29  // +checklocks:rr.s.ep.mu
    30  func (rr *renoRecovery) DoRecovery(rcvdSeg *segment, fastRetransmit bool) {
    31  	ack := rcvdSeg.ackNumber
    32  	snd := rr.s
    33  
    34  	// We are in fast recovery mode. Ignore the ack if it's out of range.
    35  	if !ack.InRange(snd.SndUna, snd.SndNxt+1) {
    36  		return
    37  	}
    38  
    39  	// Don't count this as a duplicate if it is carrying data or
    40  	// updating the window.
    41  	if rcvdSeg.logicalLen() != 0 || snd.SndWnd != rcvdSeg.window {
    42  		return
    43  	}
    44  
    45  	// Inflate the congestion window if we're getting duplicate acks
    46  	// for the packet we retransmitted.
    47  	if !fastRetransmit && ack == snd.FastRecovery.First {
    48  		// We received a dup, inflate the congestion window by 1 packet
    49  		// if we're not at the max yet. Only inflate the window if
    50  		// regular FastRecovery is in use, RFC6675 does not require
    51  		// inflating cwnd on duplicate ACKs.
    52  		if snd.SndCwnd < snd.FastRecovery.MaxCwnd {
    53  			snd.SndCwnd++
    54  		}
    55  		return
    56  	}
    57  
    58  	// A partial ack was received. Retransmit this packet and remember it
    59  	// so that we don't retransmit it again.
    60  	//
    61  	// We don't inflate the window because we're putting the same packet
    62  	// back onto the wire.
    63  	//
    64  	// N.B. The retransmit timer will be reset by the caller.
    65  	snd.FastRecovery.First = ack
    66  	snd.DupAckCount = 0
    67  	snd.resendSegment()
    68  }