Cpu is too high when hw encoding h264 interlaced video

Hi,

I'm trying to hw encoding h264 interlaced video using sample_encode in Media SDK 2013 R3 Linux Servers.  The cpu is too high about 600%. 

Compile cmd line: build.pl --cmake=intel64.make.release --build.   Encoding cmd line: sample_encode_drm h264 -tff -hw -i raw.yuv -o video.264 -w 1920 -h 1080. 

As using -tff parameter, the cpu is too high about 600%, while remove this parameter the cpu is just 30%. How can I encoding interlaced video under lower cpu?

Linux(x86_64) Intel(R) Core(TM) i7-3770T CPU @ 2.50GHz GenuineIntel GNU/Linux

Thanks,

Neil