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[client/idd] input: reduce network latency

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Route input through a dedicated high-priority stream, send pointer
motion as cumulative datagrams, and recover suspected loss reliably.

Reduce downstream input queuing with age-aware coalescing and input
thread scheduling.
This commit is contained in:
Geoffrey McRae
2026-10-08 20:34:04 +11:00
parent e30afaca2d
commit 1af2f13440
17 changed files with 3359 additions and 759 deletions
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203
idd/LGInput/CHIDDevice.cpp
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@@ -35,14 +35,15 @@ static constexpr USHORT LG_INPUT_VENDOR_ID = 0x0000;
static constexpr USHORT LG_INPUT_PRODUCT_ID = 0x0000;
static constexpr USHORT LG_INPUT_VERSION = 0x0001;
static constexpr size_t REPORT_QUEUE_LENGTH = 64;
static constexpr size_t MOTION_COALESCE_THRESHOLD =
REPORT_QUEUE_LENGTH / 2;
static constexpr size_t MOTION_EMERGENCY_DEPTH = 8;
static constexpr DWORD MOTION_AGE_BUDGET_MS = 1;
struct HIDQueuedReport
{
UCHAR data[HID_MAX_INPUT_REPORT_SIZE];
bool pureMotion;
size_t size;
UCHAR data[HID_MAX_INPUT_REPORT_SIZE];
int64_t enqueueTicks;
size_t size;
bool pureMotion;
};
struct HIDStatistics
@@ -77,6 +78,9 @@ struct HIDDeviceContext
uint16_t consumerUsage;
uint16_t absoluteX;
uint16_t absoluteY;
int64_t motionBudgetTicks;
HIDKeyboardReport keyboard;
bool keyboardValid;
HIDStatistics statistics;
HIDQueuedReport reports[REPORT_QUEUE_LENGTH];
CInputPipeClient * inputPipe;
@@ -200,28 +204,71 @@ static void RemoveQueuedReport(
--context->reportCount;
}
static bool CompactStaleMotion(
_Inout_ HIDDeviceContext * context,
_In_ UCHAR incomingReportId)
static bool MotionBudgetExceeded(_In_ HIDDeviceContext * context)
{
for (size_t i = 0; i < context->reportCount; ++i)
if (context->reportCount >= MOTION_EMERGENCY_DEPTH)
return true;
if (!context->reportCount || !context->motionBudgetTicks)
return false;
LARGE_INTEGER now = {};
if (!QueryPerformanceCounter(&now))
return false;
const int64_t oldest = GetQueuedReport(context, 0).enqueueTicks;
return oldest > 0 && now.QuadPart >= oldest &&
now.QuadPart - oldest >= context->motionBudgetTicks;
}
static bool CompactQueuedMotion(_Inout_ HIDDeviceContext * context)
{
for (size_t i = 0; i + 1 < context->reportCount; ++i)
{
HIDQueuedReport& report = GetQueuedReport(context, i);
if (!report.pureMotion ||
report.data[0] != HID_REPORT_ID_MOUSE_ABSOLUTE)
HIDQueuedReport& first = GetQueuedReport(context, i);
HIDQueuedReport& second = GetQueuedReport(context, i + 1);
if (!first.pureMotion || !second.pureMotion ||
first.data[0] != second.data[0])
continue;
bool superseded = incomingReportId == HID_REPORT_ID_MOUSE_ABSOLUTE;
for (size_t j = i + 1; !superseded && j < context->reportCount; ++j)
superseded = GetQueuedReport(context, j).data[0] ==
HID_REPORT_ID_MOUSE_ABSOLUTE;
if (superseded)
if (first.data[0] == HID_REPORT_ID_MOUSE_RELATIVE)
{
RemoveQueuedReport(context, i);
++context->statistics.staleAbsoluteCompacted;
HIDMouseRelativeReport * previous =
reinterpret_cast<HIDMouseRelativeReport *>(first.data);
const HIDMouseRelativeReport * current =
reinterpret_cast<const HIDMouseRelativeReport *>(second.data);
const int32_t x =
static_cast<int32_t>(previous->x) + current->x;
const int32_t y =
static_cast<int32_t>(previous->y) + current->y;
if (x < INT16_MIN || x > INT16_MAX ||
y < INT16_MIN || y > INT16_MAX ||
previous->buttons != current->buttons ||
previous->wheel || current->wheel)
continue;
previous->x = static_cast<int16_t>(x);
previous->y = static_cast<int16_t>(y);
RemoveQueuedReport(context, i + 1);
++context->statistics.relativeCoalesced;
return true;
}
if (first.data[0] != HID_REPORT_ID_MOUSE_ABSOLUTE)
continue;
const HIDMouseAbsoluteReport * previous =
reinterpret_cast<const HIDMouseAbsoluteReport *>(first.data);
const HIDMouseAbsoluteReport * current =
reinterpret_cast<const HIDMouseAbsoluteReport *>(second.data);
if (previous->buttons != current->buttons ||
previous->wheel || current->wheel)
continue;
CopyMemory(first.data, second.data, second.size);
first.size = second.size;
RemoveQueuedReport(context, i + 1);
++context->statistics.staleAbsoluteCompacted;
return true;
}
return false;
}
@@ -232,7 +279,13 @@ static NTSTATUS QueueReport(
_In_ size_t size,
_In_ bool pureMotion)
{
const UCHAR reportId = *static_cast<const UCHAR *>(data);
const UCHAR reportId = *static_cast<const UCHAR *>(data);
const bool motionBudgetExceeded = MotionBudgetExceeded(context);
if (motionBudgetExceeded)
while (CompactQueuedMotion(context))
{
}
if (context->reportCount)
{
HIDQueuedReport& tail =
@@ -240,20 +293,21 @@ static NTSTATUS QueueReport(
if (tail.data[0] == reportId)
{
if (reportId == HID_REPORT_ID_MOUSE_RELATIVE &&
context->reportCount >= MOTION_COALESCE_THRESHOLD &&
tail.pureMotion && pureMotion)
tail.pureMotion && pureMotion &&
motionBudgetExceeded)
{
HIDMouseRelativeReport * previous =
HIDMouseRelativeReport * previous =
reinterpret_cast<HIDMouseRelativeReport *>(tail.data);
const HIDMouseRelativeReport * current =
const HIDMouseRelativeReport * current =
static_cast<const HIDMouseRelativeReport *>(data);
const int32_t x = static_cast<int32_t>(previous->x) +
current->x;
const int32_t y = static_cast<int32_t>(previous->y) +
current->y;
const int32_t x =
static_cast<int32_t>(previous->x) + current->x;
const int32_t y =
static_cast<int32_t>(previous->y) + current->y;
if (x >= INT16_MIN && x <= INT16_MAX &&
y >= INT16_MIN && y <= INT16_MAX &&
previous->buttons == current->buttons)
previous->buttons == current->buttons &&
!previous->wheel && !current->wheel)
{
previous->x = static_cast<int16_t>(x);
previous->y = static_cast<int16_t>(y);
@@ -266,9 +320,10 @@ static NTSTATUS QueueReport(
{
const HIDMouseAbsoluteReport * previous =
reinterpret_cast<const HIDMouseAbsoluteReport *>(tail.data);
const HIDMouseAbsoluteReport * current =
const HIDMouseAbsoluteReport * current =
static_cast<const HIDMouseAbsoluteReport *>(data);
if (previous->buttons == current->buttons)
if (previous->buttons == current->buttons &&
!previous->wheel && !current->wheel)
{
CopyMemory(tail.data, data, size);
tail.size = size;
@@ -276,30 +331,24 @@ static NTSTATUS QueueReport(
return STATUS_SUCCESS;
}
}
else if (reportId == HID_REPORT_ID_KEYBOARD &&
tail.size == size && memcmp(tail.data, data, size) == 0)
{
++context->statistics.keyboardDuplicates;
return STATUS_SUCCESS;
}
}
}
if (context->reportCount == REPORT_QUEUE_LENGTH)
{
if (!CompactStaleMotion(context, reportId))
{
++context->statistics.overflows;
return STATUS_BUFFER_OVERFLOW;
}
++context->statistics.overflows;
return STATUS_BUFFER_OVERFLOW;
}
const size_t index =
const size_t index =
(context->reportHead + context->reportCount) % REPORT_QUEUE_LENGTH;
HIDQueuedReport * report = &context->reports[index];
HIDQueuedReport * report = &context->reports[index];
LARGE_INTEGER enqueueTime = {};
QueryPerformanceCounter(&enqueueTime);
CopyMemory(report->data, data, size);
report->size = size;
report->pureMotion = pureMotion;
report->enqueueTicks = enqueueTime.QuadPart;
report->size = size;
report->pureMotion = pureMotion;
++context->reportCount;
++context->statistics.queued;
if (context->reportCount > context->statistics.queueHighWater)
@@ -365,10 +414,11 @@ static NTSTATUS DeactivateDevice(
if (context->deactivateRequest)
return STATUS_DEVICE_BUSY;
context->active = false;
context->reportHead = 0;
context->reportCount = 0;
context->consumerUsage = UINT16_MAX;
context->active = false;
context->reportHead = 0;
context->reportCount = 0;
context->consumerUsage = UINT16_MAX;
context->keyboardValid = false;
}
context->deactivateRequest = request;
@@ -432,10 +482,23 @@ NTSTATUS CHIDDevice::Create(_Inout_ PWDFDEVICE_INIT deviceInit)
if (!NT_SUCCESS(status))
return status;
HIDDeviceContext * context = HIDGetDeviceContext(device);
HIDDeviceContext * context = HIDGetDeviceContext(device);
LARGE_INTEGER performanceFrequency = {};
new (context) HIDDeviceContext {};
context->active = true;
context->inputPipe = new (std::nothrow) CInputPipeClient;
if (QueryPerformanceFrequency(&performanceFrequency))
{
static_assert(MOTION_AGE_BUDGET_MS &&
1000 % MOTION_AGE_BUDGET_MS == 0,
"motion age budget must evenly divide one second");
const int64_t budgetDivisor = 1000 / MOTION_AGE_BUDGET_MS;
context->motionBudgetTicks =
performanceFrequency.QuadPart / budgetDivisor;
if (performanceFrequency.QuadPart % budgetDivisor)
++context->motionBudgetTicks;
}
context->active = true;
context->consumerUsage = UINT16_MAX;
context->inputPipe = new (std::nothrow) CInputPipeClient;
if (!context->inputPipe)
return STATUS_INSUFFICIENT_RESOURCES;
@@ -503,6 +566,13 @@ NTSTATUS CHIDDevice::SubmitReport(
++context->statistics.consumerDuplicates;
return STATUS_SUCCESS;
}
if (reportId == HID_REPORT_ID_KEYBOARD &&
context->keyboardValid &&
memcmp(&context->keyboard, report, size) == 0)
{
++context->statistics.keyboardDuplicates;
return STATUS_SUCCESS;
}
bool pureMotion = false;
switch (reportId)
@@ -573,6 +643,11 @@ NTSTATUS CHIDDevice::SubmitReport(
static_cast<const HIDConsumerReport *>(report)->usage;
break;
case HID_REPORT_ID_KEYBOARD:
CopyMemory(&context->keyboard, report, size);
context->keyboardValid = true;
break;
default:
break;
}
@@ -608,12 +683,13 @@ NTSTATUS CHIDDevice::ResetReports()
absoluteX = context->absoluteX;
absoluteY = context->absoluteY;
context->statistics.resetDiscarded += context->reportCount;
context->reportHead = 0;
context->reportCount = 0;
context->mouseMode = 0;
context->relativeButtons = 0;
context->absoluteButtons = 0;
context->consumerUsage = UINT16_MAX;
context->reportHead = 0;
context->reportCount = 0;
context->mouseMode = 0;
context->relativeButtons = 0;
context->absoluteButtons = 0;
context->consumerUsage = UINT16_MAX;
context->keyboardValid = false;
}
const HIDKeyboardReport keyboard = {
@@ -804,9 +880,10 @@ VOID HIDEvtReportQueueCleanup(_In_ WDFOBJECT object)
CSRWExclusiveLock lifecycleLock(context->lifecycleLock);
{
CSRWExclusiveLock reportLock(context->reportLock);
context->stopping = true;
context->reportHead = 0;
context->reportCount = 0;
context->stopping = true;
context->reportHead = 0;
context->reportCount = 0;
context->keyboardValid = false;
}
deactivateRequest = context->deactivateRequest;
context->deactivateRequest = nullptr;