From 2db579fdc8ece15295b931b842bf8e8eaa17c779 Mon Sep 17 00:00:00 2001 From: Marten Seemann Date: Wed, 22 Jul 2020 12:10:05 +0700 Subject: [PATCH] remove the SSLR (slow start large reduction) experiment We apparently copied that code over from Chromium's Cubic implementation, but we certainly don't need it. --- internal/congestion/cubic_sender.go | 25 +------- internal/congestion/cubic_sender_test.go | 78 ------------------------ 2 files changed, 1 insertion(+), 102 deletions(-) diff --git a/internal/congestion/cubic_sender.go b/internal/congestion/cubic_sender.go index 758399ce..7afa0531 100644 --- a/internal/congestion/cubic_sender.go +++ b/internal/congestion/cubic_sender.go @@ -40,9 +40,6 @@ type cubicSender struct { // Used for stats collection of slowstartPacketsLost lastCutbackExitedSlowstart bool - // When true, exit slow start with large cutback of congestion window. - slowStartLargeReduction bool - // Congestion window in packets. congestionWindow protocol.ByteCount @@ -63,8 +60,6 @@ type cubicSender struct { initialCongestionWindow protocol.ByteCount initialMaxCongestionWindow protocol.ByteCount - - minSlowStartExitWindow protocol.ByteCount } var _ SendAlgorithm = &cubicSender{} @@ -167,24 +162,11 @@ func (c *cubicSender) OnPacketLost( // TCP NewReno (RFC6582) says that once a loss occurs, any losses in packets // already sent should be treated as a single loss event, since it's expected. if packetNumber <= c.largestSentAtLastCutback { - if c.lastCutbackExitedSlowstart { - if c.slowStartLargeReduction { - // Reduce congestion window by lost_bytes for every loss. - c.congestionWindow = utils.MaxByteCount(c.congestionWindow-lostBytes, c.minSlowStartExitWindow) - c.slowStartThreshold = c.congestionWindow - } - } return } c.lastCutbackExitedSlowstart = c.InSlowStart() - // TODO(chromium): Separate out all of slow start into a separate class. - if c.slowStartLargeReduction && c.InSlowStart() { - if c.congestionWindow >= 2*c.initialCongestionWindow { - c.minSlowStartExitWindow = c.congestionWindow / 2 - } - c.congestionWindow -= maxDatagramSize - } else if c.reno { + if c.reno { c.congestionWindow = protocol.ByteCount(float32(c.congestionWindow) * c.renoBeta()) } else { c.congestionWindow = c.cubic.CongestionWindowAfterPacketLoss(c.congestionWindow) @@ -295,8 +277,3 @@ func (c *cubicSender) OnConnectionMigration() { c.slowStartThreshold = c.initialMaxCongestionWindow c.maxCongestionWindow = c.initialMaxCongestionWindow } - -// SetSlowStartLargeReduction allows enabling the SSLR experiment -func (c *cubicSender) SetSlowStartLargeReduction(enabled bool) { - c.slowStartLargeReduction = enabled -} diff --git a/internal/congestion/cubic_sender_test.go b/internal/congestion/cubic_sender_test.go index 2f640265..6b1acbe4 100644 --- a/internal/congestion/cubic_sender_test.go +++ b/internal/congestion/cubic_sender_test.go @@ -187,84 +187,6 @@ var _ = Describe("Cubic Sender", func() { Expect(sender.hybridSlowStart.Started()).To(BeFalse()) }) - It("slow start packet loss with large reduction", func() { - sender.SetSlowStartLargeReduction(true) - - sender.SetNumEmulatedConnections(1) - const numberOfAcks = 10 - for i := 0; i < numberOfAcks; i++ { - // Send our full send window. - SendAvailableSendWindow() - AckNPackets(2) - } - SendAvailableSendWindow() - expectedSendWindow := defaultWindowTCP + (maxDatagramSize * 2 * numberOfAcks) - Expect(sender.GetCongestionWindow()).To(Equal(expectedSendWindow)) - - // Lose a packet to exit slow start. We should now have fallen out of - // slow start with a window reduced by 1. - LoseNPackets(1) - expectedSendWindow -= maxDatagramSize - Expect(sender.GetCongestionWindow()).To(Equal(expectedSendWindow)) - - // Lose 5 packets in recovery and verify that congestion window is reduced - // further. - LoseNPackets(5) - expectedSendWindow -= 5 * maxDatagramSize - Expect(sender.GetCongestionWindow()).To(Equal(expectedSendWindow)) - - packetsInRecoveryWindow := expectedSendWindow / maxDatagramSize - - // Recovery phase. We need to ack every packet in the recovery window before - // we exit recovery. - numberOfPacketsInWindow := expectedSendWindow / maxDatagramSize - AckNPackets(int(packetsInRecoveryWindow)) - SendAvailableSendWindow() - Expect(sender.GetCongestionWindow()).To(Equal(expectedSendWindow)) - - // We need to ack the rest of the window before cwnd increases by 1. - AckNPackets(int(numberOfPacketsInWindow - 1)) - SendAvailableSendWindow() - Expect(sender.GetCongestionWindow()).To(Equal(expectedSendWindow)) - - // Next ack should increase cwnd by 1. - AckNPackets(1) - expectedSendWindow += maxDatagramSize - Expect(sender.GetCongestionWindow()).To(Equal(expectedSendWindow)) - - // Now RTO and ensure slow start gets reset. - Expect(sender.hybridSlowStart.Started()).To(BeTrue()) - sender.OnRetransmissionTimeout(true) - Expect(sender.hybridSlowStart.Started()).To(BeFalse()) - }) - - It("slow start half packet loss with large reduction", func() { - sender.SetSlowStartLargeReduction(true) - - sender.SetNumEmulatedConnections(1) - const numberOfAcks = 10 - for i := 0; i < numberOfAcks; i++ { - // Send our full send window in half sized packets. - SendAvailableSendWindowLen(maxDatagramSize / 2) - AckNPackets(2) - } - SendAvailableSendWindowLen(maxDatagramSize / 2) - expectedSendWindow := defaultWindowTCP + (maxDatagramSize * 2 * numberOfAcks) - Expect(sender.GetCongestionWindow()).To(Equal(expectedSendWindow)) - - // Lose a packet to exit slow start. We should now have fallen out of - // slow start with a window reduced by 1. - LoseNPackets(1) - expectedSendWindow -= maxDatagramSize - Expect(sender.GetCongestionWindow()).To(Equal(expectedSendWindow)) - - // Lose 10 packets in recovery and verify that congestion window is reduced - // by 5 packets. - LoseNPacketsLen(10, maxDatagramSize/2) - expectedSendWindow -= 5 * maxDatagramSize - Expect(sender.GetCongestionWindow()).To(Equal(expectedSendWindow)) - }) - It("slow start packet loss PRR", func() { sender.SetNumEmulatedConnections(1) // Test based on the first example in RFC6937.