title: glBufferSubData is very slow on many android device
body: <p>I have requested about 2M gl buffers for share, and update the data for vertex and index with glBufferSubData, it works fine on my iOS devices. while, when I test it on my android devices, it very very slow.</p>
  
  <p>I have found some notes from the official website:
  <a href="https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glBufferSubData.xhtml" rel="nofollow noreferrer">https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glBufferSubData.xhtml</a> </p>
  
  <p>what does "that rendering must drain from the pipeline before the data store can be updated" really mean?</p>