Hi Anders, The OSG support multi-threaded usage, and the time code happens in both the main threads and the cull-draw ones, one can't just limit timer calls to one thread. Setting process affinity is now supported, in particular with osgViewer, but the timer calls are still called from different threads, so I don't think this will solve much.
Perhaps one could multi-buffer the Timer so there is one per thread, I don't know how we'd go about this, or whether it would work. Is the problem that QueryPerformanceCounter()'s base offset changes per core? If so the the multi-buffering might work, but... how would you syncronize the various buffers so that they all tell the same time? Clamping times won't really solve anything as the time will still be wrong, just not negatively wrong. Robert. On 3/7/07, Anders Backman <[EMAIL PROTECTED]> wrote:
Is there anyone out there experiencing strange hang and timing problems on dual CPU/Core/HT windows XP machines? except for the ordinary laptop-timing problems of course ;-) Im currently debugging something that gives me gray hair, and someone suggested that it could be a potential problem coming from the fact that QueryPerformanceCounter() is used (osg::Timer) I have an app that runs just fine for a while (can be 1 minute, sometimes 30) and then it hangs, and it never occurs in debug-mode (of course!) so its quite tricky find the cause for it. I have already found one reason for the hangs, and that was in Producer where a OpenGL timer query never returned....But that is fixed (by skipping after 1000 iterations). It seems to be quite a few developers with this problem when I searched the web. For example: http://www.virtualdub.org/blog/pivot/entry.php?id=106 It seems that when a thread is moved in and out between different execution cores/CPU:s it can drop timing or even get negative timing results.... It also talks about hangs (which I guess could be a second order problem that comes from the timing problem). Right now Im looking at something that looks like a hang inside osg::Timer::tick() So is there anyone else experiencing this? There is a bunch of recommendations from MS: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/directx9_c/Game_Timing_and_Multicore_Processors.asp - using QueryPerformanceCounter from only one thread - setting SetThreadAffinityMask so that the timing thread runs on only one CPU/Core - clamping the subtraction result so you never get a negative one: inline double delta_s( Timer_t t1, Timer_t t2 ) const { return (double)(t2 - t1)*_secsPerTick; } Should be: inline double delta_s( Timer_t t1, Timer_t t2 ) const { return (double)osg::clampAbove((t2 - t1), 0)*_secsPerTick; } -- ________________________________________________________________ Anders Backman Email: [EMAIL PROTECTED] HPC2N/VRlab Phone: +46 (0)90-786 9936 Umea university Cellular: +46 (0)70-392 64 67 S-901 87 UMEA SWEDEN Fax: +46 90-786 6126 http://www.cs.umu.se/~andersb _______________________________________________ osg-users mailing list [email protected] http://openscenegraph.net/mailman/listinfo/osg-users http://www.openscenegraph.org/
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