# Problem to use Asynchronous execution with PBO **URL:** \ **Category:** CUDA Programming and Performance\ **Created:** [March 4, 2008, 11:33am UTC](https://forums.developer.nvidia.com/t/problem-to-use-asynchronous-execution-with-pbo/2876 "2008-03-04T11:33:06Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![spacerat](https://developer.download.nvidia.com/images/forums/profile-default-devtalk-84.png) [@spacerat](https://forums.developer.nvidia.com/u/spacerat)\ **Post date:** [March 4, 2008, 11:33am UTC](https://forums.developer.nvidia.com/t/problem-to-use-asynchronous-execution-with-pbo/2876/1 "2008-03-04T11:33:06Z")
I am trying to optimize may raycaster and found a couple of difficulties - I hope somebody can give me a good advice. I seems the driver always stalls making CUDA calls. I always get framerates like 60,30,20,15,12,… but there is nothing in between, it basically snaps. (Its not the VSync - I already switched that off) I guess the problem is that I was not using the Asynchronous versions with events. I therefore modified everything and found another problem which I guess could be a driver bug or undocumented problem… If I want to use a mapped PBO along with the async code, the GPU seems to be doing nothing. * * * Here what happens without PBO’s: * * * ```auto ... asyncAPI_test() ... ``` Result:OK time spent executing by the GPU: 181.57 time spent by CPU in CUDA calls: 0.11 CPU executed 354 iterations while waiting for GPU to finish Test PASSED * * * Here what happens with PBO’s: * * * ```auto ... CUDA_SAFE_CALL(cudaGLMapBufferObject( (void**)&out_data, pbo_out));   asyncAPI_test() CUDA_SAFE_CALL(cudaGLUnmapBufferObject( pbo_out)); ... ``` Result:Failed Test FAILED time spent executing by the GPU: 0.00 time spent by CPU in CUDA calls: 2.19 CPU executed 0 iterations while waiting for GPU to finish any help is appreciated… regards ---
**Author:** ![wumpus](https://sea2.discourse-cdn.com/nvidia/user_avatar/forums.developer.nvidia.com/wumpus/32/12040_2.png) [@wumpus](https://forums.developer.nvidia.com/u/wumpus)\ **Post date:** [March 4, 2008, 11:54am UTC](https://forums.developer.nvidia.com/t/problem-to-use-asynchronous-execution-with-pbo/2876/2 "2008-03-04T11:54:08Z")
I do know that OpenGL calls always cause an implicit synchronisation when switching context (like when using CUDA), so using async calls together with OpenGL interoperability is only of limited use. ---
**Author:** ![spacerat](https://developer.download.nvidia.com/images/forums/profile-default-devtalk-84.png) [@spacerat](https://forums.developer.nvidia.com/u/spacerat)\ **Post date:** [March 4, 2008, 11:59am UTC](https://forums.developer.nvidia.com/t/problem-to-use-asynchronous-execution-with-pbo/2876/3 "2008-03-04T11:59:58Z")
> [@](#): > > I do know that OpenGL calls always cause an implicit synchronisation when switching context (like when using CUDA), so using async calls together with OpenGL interoperability is only of limited use. > > [snapback]337442[/snapback] Um… does it means it is impossible ? Or is there any other possiblity to change the driver’s synchronization behavior? It seems that there is an internal waiting loop synchronized to 60 fps… I just want to get optimal performance. ---
**Author:** ![wumpus](https://sea2.discourse-cdn.com/nvidia/user_avatar/forums.developer.nvidia.com/wumpus/32/12040_2.png) [@wumpus](https://forums.developer.nvidia.com/u/wumpus)\ **Post date:** [March 4, 2008, 12:09pm UTC](https://forums.developer.nvidia.com/t/problem-to-use-asynchronous-execution-with-pbo/2876/4 "2008-03-04T12:09:03Z")
Well I mean that you can do it, it just doesn’t help performance. But the 60fps number is strange, CUDA shouldn’t lock it to a certain number of frames per second. I’ve had much higher fps rates with CUDA-using opengl programs. ---
**Author:** ![spacerat](https://developer.download.nvidia.com/images/forums/profile-default-devtalk-84.png) [@spacerat](https://forums.developer.nvidia.com/u/spacerat)\ **Post date:** [March 4, 2008, 12:43pm UTC](https://forums.developer.nvidia.com/t/problem-to-use-asynchronous-execution-with-pbo/2876/5 "2008-03-04T12:43:51Z")
> [@](#): > > Well I mean that you can do it, it just doesn’t help performance. > > But the 60fps number is strange, CUDA shouldn’t lock it to a certain number of frames per second. I’ve had much higher fps rates with CUDA-using opengl programs. > > [snapback]337445[/snapback] Hm… its not just my program. In the SDK examples there is already a fluid demo that is showing the FPS. In my case its always 60.8 even I reduce the number of particles to a fraction of the original amount. The strange thing is now: Once I start dragging the console window accross the GL-Window, the framerate increases from 60.8 up to 97 fps … ??? The only thing I can guess is that the synchronization is done event based and each times an event (like whatever) occurs, the synchronization checks if the GPU is done… ---
**Author:** ![spacerat](https://developer.download.nvidia.com/images/forums/profile-default-devtalk-84.png) [@spacerat](https://forums.developer.nvidia.com/u/spacerat)\ **Post date:** [March 4, 2008, 1:06pm UTC](https://forums.developer.nvidia.com/t/problem-to-use-asynchronous-execution-with-pbo/2876/6 "2008-03-04T13:06:32Z")
I just found out that in my case, already keeping a key pushed leads to a higher framerate … Its really an event-problem. Is it possible to generate fake-key events e.g. in a timer loop ? ---
**Author:** ![MisterAnderson42](https://developer.download.nvidia.com/images/forums/profile-default-devtalk-84.png) [@MisterAnderson42](https://forums.developer.nvidia.com/u/MisterAnderson42)\ **Post date:** [March 4, 2008, 2:58pm UTC](https://forums.developer.nvidia.com/t/problem-to-use-asynchronous-execution-with-pbo/2876/7 "2008-03-04T14:58:56Z")
What event system are you using? In windows you usually do these things in the Idle event. I seem to recall there being a return value that controlled how long it will be until the next idle event.