diff --git a/src/core/ack_tracker.c b/src/core/ack_tracker.c
index 6e34cc9f57..e0df5b047c 100644
--- a/src/core/ack_tracker.c
+++ b/src/core/ack_tracker.c
@@ -179,19 +179,21 @@ QuicAckTrackerAckPacket(
//
// There are several conditions where we decide to send an ACK immediately:
//
- // 1. We have received 'PacketTolerance' ACK eliciting packets.
- // 2. We received an ACK eliciting packet that doesn't directly follow the
+ // 1. The packet included an IMMEDIATE_ACK frame.
+ // 2. ACK delay is disabled (MaxAckDelayMs == 0).
+ // 3. We have received 'PacketTolerance' ACK eliciting packets.
+ // 4. We received an ACK eliciting packet that doesn't directly follow the
// previously received packet number. So we assume there might have
// been loss and should indicate this info to the peer. This logic is
// disabled if 'IgnoreReordering' is TRUE.
- // 3. The delayed ACK timer fires after the configured time.
- // 4. The packet included an IMMEDIATE_ACK frame.
+ // 5. The delayed ACK timer fires after the configured time.
//
// If we don't queue an immediate ACK and this is the first ACK eliciting
// packet received, we make sure the ACK delay timer is started.
//
if (AckType == QUIC_ACK_TYPE_ACK_IMMEDIATE ||
+ Connection->Settings.MaxAckDelayMs == 0 ||
(Tracker->AckElicitingPacketsToAcknowledge >= (uint16_t)Connection->PacketTolerance) ||
(!Connection->State.IgnoreReordering &&
(NewLargestPacketNumber &&
@@ -200,9 +202,7 @@ QuicAckTrackerAckPacket(
&Tracker->PacketNumbersToAck,
QuicRangeSize(&Tracker->PacketNumbersToAck) - 1)->Count == 1))) { // The gap is right before the last packet number.
//
- // Always send an ACK immediately if we have received enough ACK
- // eliciting packets OR the latest one indicate a gap in the packet
- // numbers, which likely means there was loss.
+ // Send the ACK immediately.
//
QuicSendSetSendFlag(&Connection->Send, QUIC_CONN_SEND_FLAG_ACK);
diff --git a/src/core/connection.c b/src/core/connection.c
index 96f8ec7b70..24720f8fc6 100644
--- a/src/core/connection.c
+++ b/src/core/connection.c
@@ -2349,9 +2349,11 @@ QuicConnGenerateLocalTransportParameters(
MaxUdpPayloadSizeFromMTU(
CxPlatSocketGetLocalMtu(
Connection->Paths[0].Binding->Socket));
- LocalTP->MaxAckDelay =
- Connection->Settings.MaxAckDelayMs + MsQuicLib.TimerResolutionMs;
- LocalTP->MinAckDelay = MS_TO_US(MsQuicLib.TimerResolutionMs);
+ LocalTP->MaxAckDelay = QuicConnGetAckDelay(Connection);
+ LocalTP->MinAckDelay =
+ MsQuicLib.ExecutionConfig != NULL &&
+ MsQuicLib.ExecutionConfig->PollingIdleTimeoutUs != 0 ?
+ 0 : MS_TO_US(MsQuicLib.TimerResolutionMs);
LocalTP->ActiveConnectionIdLimit = QUIC_ACTIVE_CONNECTION_ID_LIMIT;
LocalTP->Flags =
QUIC_TP_FLAG_INITIAL_MAX_DATA |
@@ -5296,7 +5298,9 @@ QuicConnRecvFrames(
Connection->NextRecvAckFreqSeqNum = Frame.SequenceNumber + 1;
Connection->State.IgnoreReordering = Frame.IgnoreOrder;
- if (Frame.UpdateMaxAckDelay < 1000) {
+ if (Frame.UpdateMaxAckDelay == 0) {
+ Connection->Settings.MaxAckDelayMs = 0;
+ } else if (Frame.UpdateMaxAckDelay < 1000) {
Connection->Settings.MaxAckDelayMs = 1;
} else {
CXPLAT_DBG_ASSERT(US_TO_MS(Frame.UpdateMaxAckDelay) <= UINT32_MAX);
@@ -5318,7 +5322,7 @@ QuicConnRecvFrames(
case QUIC_FRAME_IMMEDIATE_ACK: // Always accept the frame, because we always enable support.
AckImmediately = TRUE;
break;
-
+
case QUIC_FRAME_TIMESTAMP: { // Always accept the frame, because we always enable support.
if (!Connection->State.TimestampRecvNegotiated) {
QuicTraceEvent(
@@ -5345,7 +5349,7 @@ QuicConnRecvFrames(
Packet->SendTimestamp = Frame.Timestamp;
break;
}
-
+
default:
//
// No default case necessary, as we have already validated the frame
diff --git a/src/core/connection.h b/src/core/connection.h
index 977e70cdb4..4cb58c69f2 100644
--- a/src/core/connection.h
+++ b/src/core/connection.h
@@ -1353,6 +1353,26 @@ QuicConnTimerExpired(
_In_ uint64_t TimeNow
);
+_IRQL_requires_max_(PASSIVE_LEVEL)
+inline
+uint64_t
+QuicConnGetAckDelay(
+ _In_ const QUIC_CONNECTION* Connection
+ )
+{
+ if (Connection->Settings.MaxAckDelayMs &&
+ (MsQuicLib.ExecutionConfig == NULL ||
+ Connection->Settings.MaxAckDelayMs > US_TO_MS(MsQuicLib.ExecutionConfig->PollingIdleTimeoutUs))) {
+ //
+ // If we are using delayed ACKs, and the ACK delay is greater than the
+ // polling timeout, then we need to account for delay resulting from
+ // from the timer resolution.
+ //
+ return (uint64_t)Connection->Settings.MaxAckDelayMs + (uint64_t)MsQuicLib.TimerResolutionMs;
+ }
+ return (uint64_t)Connection->Settings.MaxAckDelayMs;
+}
+
//
// Called when the QUIC version is set.
//
diff --git a/src/core/inline.c b/src/core/inline.c
index fbc50207ef..df2825c02b 100644
--- a/src/core/inline.c
+++ b/src/core/inline.c
@@ -779,6 +779,11 @@ QuicConnTimerSet(
_In_ uint64_t DelayUs
);
+uint64_t
+QuicConnGetAckDelay(
+ _In_ const QUIC_CONNECTION* Connection
+ );
+
uint8_t
QuicPacketTraceType(
_In_ const QUIC_SENT_PACKET_METADATA* Metadata
diff --git a/src/core/send.c b/src/core/send.c
index 0fcc615c7a..6b439482c8 100644
--- a/src/core/send.c
+++ b/src/core/send.c
@@ -870,10 +870,7 @@ QuicSendWriteFrames(
QUIC_ACK_FREQUENCY_EX Frame;
Frame.SequenceNumber = Connection->SendAckFreqSeqNum;
Frame.PacketTolerance = Connection->PeerPacketTolerance;
- Frame.UpdateMaxAckDelay =
- MS_TO_US(
- (uint64_t)Connection->Settings.MaxAckDelayMs +
- (uint64_t)MsQuicLib.TimerResolutionMs);
+ Frame.UpdateMaxAckDelay = MS_TO_US(QuicConnGetAckDelay(Connection));
Frame.IgnoreOrder = FALSE;
Frame.IgnoreCE = FALSE;
@@ -1489,6 +1486,7 @@ QuicSendStartDelayedAckTimer(
{
QUIC_CONNECTION* Connection = QuicSendGetConnection(Send);
+ CXPLAT_DBG_ASSERT(Connection->Settings.MaxAckDelayMs != 0);
if (!Send->DelayedAckTimerActive &&
!(Send->SendFlags & QUIC_CONN_SEND_FLAG_ACK) &&
!Connection->State.ClosedLocally &&