!00% CPU when run 640x480

[hannesa2]

When I run

pi@car ~ $ mjpg_streamer -i '/usr/local/lib/input_uvc.so -q 85 -r 640x480 -fps 15' -o /usr/local/lib/output_http.so
[1] 1366
pi@car ~ $ MJPG Streamer Version: git rev: 310b29f4a94c46652b20c4b7b6e5cf24e532af39
 i: Using V4L2 device.: /dev/video0
 i: Desired Resolution: 640 x 480
 i: Frames Per Second.: 15
 i: Format............: YUV
 i: JPEG Quality......: 80
Adding control for Pan (relative)
UVCIOC_CTRL_ADD - Error: Inappropriate ioctl for device
Adding control for Tilt (relative)
UVCIOC_CTRL_ADD - Error: Inappropriate ioctl for device
Adding control for Pan Reset
UVCIOC_CTRL_ADD - Error: Inappropriate ioctl for device
Adding control for Tilt Reset
UVCIOC_CTRL_ADD - Error: Inappropriate ioctl for device
Adding control for Pan/tilt Reset
UVCIOC_CTRL_ADD - Error: Inappropriate ioctl for device
Adding control for Focus (absolute)
UVCIOC_CTRL_ADD - Error: Inappropriate ioctl for device
mapping control for Pan (relative)
UVCIOC_CTRL_MAP - Error: Inappropriate ioctl for device
mapping control for Tilt (relative)
UVCIOC_CTRL_MAP - Error: Inappropriate ioctl for device
mapping control for Pan Reset
UVCIOC_CTRL_MAP - Error: Inappropriate ioctl for device
mapping control for Tilt Reset
UVCIOC_CTRL_MAP - Error: Inappropriate ioctl for device
mapping control for Pan/tilt Reset
UVCIOC_CTRL_MAP - Error: Inappropriate ioctl for device
mapping control for Focus (absolute)
UVCIOC_CTRL_MAP - Error: Inappropriate ioctl for device
mapping control for LED1 Mode
UVCIOC_CTRL_MAP - Error: Inappropriate ioctl for device
mapping control for LED1 Frequency
UVCIOC_CTRL_MAP - Error: Inappropriate ioctl for device
mapping control for Disable video processing
UVCIOC_CTRL_MAP - Error: Inappropriate ioctl for device
mapping control for Raw bits per pixel
UVCIOC_CTRL_MAP - Error: Inappropriate ioctl for device
 o: www-folder-path...: disabled
 o: HTTP TCP port.....: 8080
 o: username:password.: disabled
 o: commands..........: enabled

CPU hat a 100% load
But when I run instead
mjpg_streamer -i '/usr/local/lib/input_uvc.so -q 85 -r 640x480 -fps 15' -o /usr/local/lib/output_http.so
this
mjpg_streamer -i '/usr/local/lib/input_uvc.so -q 85 -r 570x259 -fps 15' -o /usr/local/lib/output_http.so

I see just 15-20% CPU load.
Who understands this, or how to run 640x480 with less CPU load ?