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[Windows/HIP] Fix APU large BAR detection to enable >64GB unified memory allocation #4077

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[Windows/HIP] Fix APU large BAR detection to enable >64GB unified memory allocation #4077

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7 changes: 4 additions & 3 deletions projects/clr/rocclr/device/pal/paldevice.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -615,9 +615,10 @@ void NullDevice::fillDeviceInfo(const Pal::DeviceProperties& palProp,
info_.aqlBarrierValue_ = true;

#if defined(_WIN64)
if (amd::IS_HIP) {

@gandryey gandryey Mar 26, 2026

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There was a reason why large bar was disabled at least on dgpu systems, because HIP expects CPU access to the device memory, but in Windows it's not possible. We may have regressions after this change or extra fixes in the tests.

info_.largeBar_ = false;
} else if (heaps[Pal::GpuHeapInvisible].logicalSize == 0) {
// For APU/integrated devices (no invisible/private VRAM heap), treat as large bar.
// This applies to both HIP and OpenCL: on UMA systems the entire system memory is
// GPU-local, so resizable BAR semantics apply.
if (heaps[Pal::GpuHeapInvisible].logicalSize == 0) {
info_.largeBar_ = true;
ClPrint(amd::LOG_INFO, amd::LOG_INIT, "Resizable bar enabled");
}
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5 changes: 4 additions & 1 deletion projects/clr/rocclr/device/pal/palmemory.cpp
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Expand Up @@ -116,7 +116,10 @@ bool Memory::create(Resource::MemoryType memType, Resource::CreateParams* params
memType = Persistent;
}

if (amd::IS_HIP && dev().settings().apuSystem_) {
if (amd::IS_HIP && dev().settings().apuSystem_ && !dev().info().largeBar_) {
// For large-bar APU (UMA, no invisible heap), skip the premature redirect to
// RemoteUSWC: the retry loop below will naturally fall through Local ->
// Persistent -> RemoteUSWC, avoiding the Windows GART 50%-of-RAM cap.
Pal::gpusize totalAlloc = dev().TotalAlloc();
if (memType == Local && totalAlloc > dev().GetMaxFrameBuffer()) {
memType = RemoteUSWC;
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