about linux sdk 1080p encoding performance

hi, all,

I tried 1080p HD source encoding with Intel HD graphic 4000  i7-3520M (ivy bridge) on ubuntu linux, however, the sample_encode_drm runs at only ~40fps avg with TU=1, and the CPU usage is about %66 of one core. 

However, according to this test, intel hd graphics 4000 should reach the speed of over 100fps:

http://www.tetrachromesoftware.com/q264Test1Analysis/q264test_4.html

I've also rebooted to windows and encode with mediacoder, the result is also ~40fps.

How could I increase encoding speed? use another CPU?