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← Stalling and Starving - Interactive 3D Graphics

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Showing Revision 2 created 05/24/2016 by Udacity Robot.

  1. So, given this pipeline that was in the quiz, we found that B is the slow stage
  2. here and B is, in fact, called the bottleneck. It's the slowest stage and it's
  3. the one that determines how fast anything is going to come out of the pipeline.
  4. And there's always a bottleneck in the pipeline. In fact, there's always some
  5. slowest stage. Maybe two or three that are tied for slowest but there's always
  6. some stage that's the slowest. Objects 3 and 4 move on through the pipeline and
  7. object 2 is still being processed by B. So, what this is called is when stage C
  8. is waiting for input and nothing's coming because we're waiting for B to finish,
  9. that's called starvation. That's where C is not getting anything until B is
  10. totally complete. On the other hand, what's happening here is stage A has
  11. finished processing object 1 but object 1 can't move on because, stage B is
  12. still processing object 2. This is called stalling. With the rendering pipeline,
  13. these same sorts of principles apply. Having the application run efficiently and
  14. keep the GPU fed with data is a common bottleneck for example. The bottleneck
  15. will change over time. With sometimes one stage being the slowest sometimes
  16. another. Gpu designers use different techniques to perform load balancing, such
  17. as first in and first out queues. Where you sort of stack up a bunch of objects
  18. so that if the stage suddenly gets faster, a bunch of objects can move into it
  19. quickly, or other techniques such as unified shaders. We wont be describing
  20. these techniques in detail in this course, but it's good to be aware that the
  21. GPU has a lot going on inside of it. Various performance debugging tools let you
  22. see what parts of the pipeline are bottlenecks and so, can help you improve the
  23. performance of your application.