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Journeyman III

Updating big textures in Crossfire configurations

Hi, everyone. In our project we are implementing clipmap technology for terrain rendering. We are using DirectX. Typical clipmap stack is implemented using Texture2DArray. For example 10 slices of 2048x2048 textures. For updating clipmap contents we are using intermediate texture created with D3D11_USAGE_DYNAMIC and  D3D11_CPU_ACCESS_WRITE flags. We lock this texture by calling Map() with D3D11_MAP_WRITE_DISCARD flag. Copy data and then call Unmap(). After this we copy data on GPU from intermediate texture to clipmap texture array using CopySubresourceRegion().

All this works quite fine on one-gpu configurations but there are noticeable lags when running on dual-gpu Radeon 6990. All multi-gpu programming guides recommend to eliminate interframe dependencies. For render targets it is highly recommended to clear them each frame but we can't something like this for texture. I suspect that problem is that after update of tiny intermediate texture and copying data to clipmap texture array on next frame second GPU copies whole modified texture array which is much bigger. Am I correct with this assumption? So my question is if there are any way not to copy whole texture array but instead do such update for second gpu. Something like say to driver not to synchronize texture array between gpus and do it manually for each gpu. Or any other way to get good smooth FPS on multigpu system. It would be really nice to get help from some AMD-guy who really knows how all this crossfire-stuff works behind scenes and could pinpoint source of the problem.

Thanks for help!

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