title: Interpretation of intel_gpu_top output
body: <p>Can anyone shed any light on the output of <code>intel_gpu_top</code>?  Specifically, what is task <em>GAM</em>, <em>VS</em> etc (The <a href="http://manpages.ubuntu.com/manpages/trusty/man1/intel_gpu_top.1.html" rel="noreferrer">man page</a> isn't much help.)</p>
  
  <p>What does <em>bitstream busy</em> mean? It always seems to be zero...</p>
  
  <pre><code>               render busy:  45%: █████████                              render space: 83/131072
              bitstream busy:   0%:                                     bitstream space: 0/131072
                blitter busy:   0%:                                       blitter space: 0/131072
  
                        task  percent busy
                         GAM:  43%: ████████▋               vert fetch: 0 (0/sec)
                          VS:  35%: ███████                 prim fetch: 0 (0/sec)
                          CL:  33%: ██████▋              VS invocations: 2101845324 (1427552/sec)
                          SF:  33%: ██████▋              GS invocations: 0 (0/sec)
                          VF:  33%: ██████▋                   GS prims: 0 (0/sec)
                        GAFS:  33%: ██████▋              CL invocations: 701123988 (475776/sec)
                         SOL:  32%: ██████▌                   CL prims: 701708489 (475888/sec)
                          GS:  32%: ██████▌              PS invocations: 1254669239424 (116548992/sec)
                          DS:  32%: ██████▌              PS depth pass: 604287310764 (222384008/sec)
                         TDG:   2%: ▌                    
                        URBM:   2%: ▌                    
                        GAFM:   1%: ▎                    
                          HS:   0%:                      
                         SVG:   0%:                      
                         VFE:   0%:                      
  </code></pre>