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Fix VkPhysicalDeviceLimits::timestampPeriod calculations on Intel GPU.

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- Guard against Intel returning zero values for CPU & GPU timestamps.
- Apply lowpass filter on timestampPeriod updates, to avoid wild temporary
  changes, particularly at startup before GPU has been really exercised.
This commit is contained in:
Bill Hollings 2023-08-17 17:47:39 -04:00
parent b3c9f867ee
commit 530bde199b
1 changed files with 17 additions and 9 deletions
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26
MoltenVK/MoltenVK/GPUObjects/MVKDevice.mm
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@ -1567,16 +1567,24 @@ VkResult MVKPhysicalDevice::getQueueFamilyProperties(uint32_t* pCount,
return rslt;
}
// Mark both CPU and GPU timestamps, and if needed, update the timestamp period for this device.
// On Apple GPUs, the CPU & GPU timestamps are the same, and the timestamp period never changes.
// If needed, update the timestamp period for this device, using a crude lowpass filter to level out
// wild temporary changes, particularly during initial queries before much GPU activity has occurred.
// On Apple GPUs, CPU & GPU timestamps are the same, and timestamp period never changes.
void MVKPhysicalDevice::updateTimestampsAndPeriod() {
if (_properties.vendorID == kAppleVendorId) {
_prevGPUTimestamp = _prevCPUTimestamp = mvkGetElapsedNanoseconds();
} else {
MTLTimestamp earlierCPUTs = _prevCPUTimestamp;
MTLTimestamp earlierGPUTs = _prevGPUTimestamp;
[_mtlDevice sampleTimestamps: &_prevCPUTimestamp gpuTimestamp: &_prevGPUTimestamp];
_properties.limits.timestampPeriod = (double)(_prevCPUTimestamp - earlierCPUTs) / (double)(_prevGPUTimestamp - earlierGPUTs);
if (_properties.vendorID == kAppleVendorId) { return; }
MTLTimestamp earlierCPUTs = _prevCPUTimestamp;
MTLTimestamp earlierGPUTs = _prevGPUTimestamp;
[_mtlDevice sampleTimestamps: &_prevCPUTimestamp gpuTimestamp: &_prevGPUTimestamp];
double elapsedCPUNanos = _prevCPUTimestamp - earlierCPUTs;
double elapsedGPUTicks = _prevGPUTimestamp - earlierGPUTs;
if (elapsedCPUNanos && elapsedGPUTicks) { // Ensure not zero
float tsPeriod = elapsedCPUNanos / elapsedGPUTicks;
// Basic lowpass filter Y = (1 - a)Y + a*X.
// The lower a is, the slower Y will change over time.
static const float a = 0.05;
_properties.limits.timestampPeriod = ((1.0 - a) * _properties.limits.timestampPeriod) + (a * tsPeriod);
}
}