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PODirectX - GetSurfaceLevel Performance Issue
 

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  1. PODirectX - GetSurfaceLevel Performance Issue
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    <p>I'm implementing deferred shading in a directx 9 application. My method of deferred shading requires 3 render targets( color, position, and normal ). It is necessary to:</p> <ol> <li>set the render targets in the device at the beginning of the 'render' function</li> <li>draw the data to them in the 'rt pass'</li> <li>remove the render targets from the device( so as not to draw over them during subsequent passes)</li> <li>set the render targets as textures for subsequent passes so that the effect can recall data 'drawn' to the rt's in the 'rt pass'...</li> </ol> <p>This method works fine, however, I am experiencing performance issues. I've narrowed them down to two function calls:</p> <pre><code>IDirect3DTexture9::GetSurfaceLevel() IDirect3DDevice9::SetRenderTarget() </code></pre> <p>Here is code to set render target:</p> <pre><code>IDirect3DDevice9 *pd3dDevice = CEffectManager::GetDevice(); IDirect3DTexture9 *pRT = CEffectManager::GetColorRT(); IDirect3DSurface9 *pSrf = NULL; pRT-&gt;GetSurfaceLevel( 0, &amp;pSrf ); pd3dDevice-&gt;SetRenderTarget( 0, pSrf ); </code></pre> <p>PIX indicates that the duration( cycles ) of the call to GetSurfaceLevel() is very high ~1/2 ms per call( Duration / Total Duration * 1 / FrameRate ). Because it is necessary to get 3 surfaces, combined, the duration is too high! Its more than 4 times greater than the combined draw calls...</p> <p>I tried to eliminate the call to GetSurfaceLevel() by storing a pointer to the surface during render target creation...oddly enough, the SetRenderTarget() function assumed the same duration( when before its duration was negligible ). Here is altered code:</p> <pre><code>IDirect3DDevice9 *pd3dDevice = CEffectManager::GetDevice(); IDirect3DSurface9 *pSrf = CEffectManager::GetColorSurface(); pd3dDevice-&gt;SetRenderTarget( 0, pSrf ); </code></pre> <p>Is there a way around this performance issue? Why does the second method take as long as the first? It seems as though the process within IDirect3DDevice9::SetRenderTarget() simply takes time...is there a device state that I can set to help performance?</p> <p>Update: I've implemented the following code in order to better test performance:</p> <pre><code>IDirect3DDevice9 *pd3dDevice = CEffectManager::GetDevice(); IDirect3DTexture9 *pRT = CEffectManager::GetColorRT(); IDirect3DSurface9 *pSRF = NULL; IDirect3DQuery9 *pEvent = NULL; LARG_INTEGER lnStart, lnStop, lnFrequency; // create query pd3dDevice-&gt;CreateQuery( D3DQUERYTYPE_EVENT, &amp;pEvent ); // insert 'end' marker pEvent-&gt;Issue( D3DISSUE_END ); // flush command buffer while( S_FALSE == pEvent-&gt;GetData( NULL, 0, D3DGETDATA_FLUSH ) ); // get start time QueryPerformanceCounter( &amp;lnStart ); // api call pRT-&gt;GetSurfaceLevel(); // insert 'end' marker pEvent-&gt;Issue( D3DISSUE_END ) // flush the command buffer while( S_FALSE == pEvent-&gt;GetData( NULL, 0, D3DGETDATA_FLUSH ) ); QueryPerformanceCounter( &amp;lnStop ); QueryPerformanceFrequency( &amp;lnFreq ); lnStop.QuadPart -= lnStart.QuadPart; float fElapsedTime = ( float )lnStop.QuadPart / ( float )lnFreq.QuadPart; </code></pre> <p>fElapsedTime on average measured 10 - 50 microseconds I performed the same test on IDirect3DDevice9::SetRenderTarget() and the results on average measured 5 - 30 microseconds...</p> <p>This data is much better than what I got from PIX...It suggests that there is not as much of a delay as I thought, however, the framerate is drastically reduced using deferred shading...this seems to be the most likely source for the loss of performance...did I effectively query the device?</p>
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    1. CODid you try timing with IDirect3DQuery9 in addition to PIX? Do you use MRT? What GPU/driver you have? Calling SetRenderTarget isn't free but shouldn't be a bottleneck for a simple deferred renderer.
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    2. COGPU: ATI Radeon HD 4550, up to 8 RTs...[GPU specs](http://www.amd.com/us/products/desktop/graphics/ati-radeon-hd-4000/hd-4550/Pages/ati-radeon-hd-4550-specifications.aspx) I will try IDirect3DQuery9 tonight...
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    3. COi've tried querying the device...my implementation was added above...better results...so long as i have correctly queried the device
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