FRHICommandListBase::LockBufferMGPU

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Description

LockBufferMGPU / UnlockBufferMGPU may ONLY be called for buffers with the EBufferUsageFlags::MultiGPUAllocate flag set! And buffers with that flag set may not call the regular (single GPU) LockBuffer / UnlockBuffer. The single GPU version of LockBuffer uses driver mirroring to propagate the updated buffer to other GPUs, while the MGPU / MultiGPUAllocate version requires the caller to manually lock and initialize the buffer separately on each GPU. This can be done by iterating over FRHIGPUMask::All() and calling LockBufferMGPU / UnlockBufferMGPU for each version.

EBufferUsageFlags::MultiGPUAllocate is only needed for cases where CPU initialized data needs to be different per GPU, which is a rare edge case. Currently, this is only used for the ray tracing acceleration structure address buffer, which contains virtual address references to other GPU resources, which may be in a different location on each GPU.

void * LockBufferMGPU  
(  
    FRHIBuffer * Buffer,  
    uint32 GPUIndex,  
    uint32 Offset,  
    uint32 SizeRHI,  
    EResourceLockMode LockMode  
)  
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void * LockBufferMGPU (     FRHIBuffer * Buffer,     uint32 GPUIndex,     uint32 Offset,     uint32 SizeRHI,     EResourceLockMode LockMode )