xrandr and xorg.conf
 

After long time searching I ended up with xrandr to manage nvidia-optimus technology and to reduce my laptop temperature according to https://nouveau.freedesktop.org/wiki/Optimus/

however, Since there is no vgaswitcheroo folder in /sys/kernel/debug directory I can't power off nvidia GPU permanently. Hence, I'm going to use X configuration files to achieve a persistent configuration for that purpose. But, I am not sure about location, name and content of the file. Is it suffice to make a file with xrandr.conf name in /etc/X11/xorg.conf.d/ with this line?
PS: based on aforementioned article, using xrandr is more suitable than bumblebee for those who want to use open source nouveau driver (kernel 3.13 and above). Perhaps it's time to modify slackdoc document about nvidia-optimus.

You can use bbswitch to switch off your NVidia GPU.

Sorry, my bad mistake. I don't want to turn of nvidia card. I want to use xrandr and DRI_PRIME to switch between GPUs instead using bumblebee and optirun. But, runing xrandr at every system reboot is tedious, so I have to create a .conf file for xorg so that it automatically offload Intel GPU. Where is the right place for such file? /etc/X11/xorg.conf.d/ or /usr/share/X11/xorg.conf.d/

you can place it on /etc/rc.d/rc.local

xrandr is an X extension. It's not possible to start is before X.

Solved. I added it to ~/.xprofile and it's working.

Just as a general point of knowledge, if you see these two types of directories (not necessarily just X11, but matching directories in /etc/ and /usr/share/, /etc/ is typically for the user to override the distro-provided /usr/share/ conf files. Keep in mind, if you edit something in /usr/share/, if you upgrade or reinstall that package, it will replace that custom file without any hesitation or prompting.

TL;DNR

/usr/share/X11/xorg.conf.d/ - system defaults - user shouldn't normally edit
/etc/X11/xorg.conf.d/ - used by user to override system defaults