我使用的是 Arch linux，笔记本电脑上有两个显卡，没有外接显示器。显卡是intel和nvidia 720M。默认使用Intel，并安装nvidia驱动程序（我认为）。这是以下的输出inxi -G：
Graphics: Card-1: Intel 3rd Gen Core processor Graphics Controller
Card-2: NVIDIA GF117M [GeForce 610M/710M/810M/820M / GT 620M/625M/630M/720M]
Display Server: X.Org 1.19.2 driver: modesetting
Resolution: [email protected]
GLX Renderer: Mesa DRI Intel Ivybridge Mobile
GLX Version: 3.0 Mesa 17.0.1
这是输出egrep 'EE|WW' /var/log/Xorg.0.log：
[ 23.642] Current Operating System: Linux redshift 4.10.2-1-ARCH #1 SMP PREEMPT Mon Mar 13 17:13:41 CET 2017 x86_64
(WW) warning, (EE) error, (NI) not implemented, (??) unknown.
[ 23.864] (WW) The directory "/usr/share/fonts/Type1/" does not exist.
[ 23.865] (WW) `fonts.dir' not found (or not valid) in "/usr/share/fonts/100dpi/".
[ 23.865] (WW) `fonts.dir' not found (or not valid) in "/usr/share/fonts/75dpi/".
[ 23.902] (WW) Open ACPI failed (/var/run/acpid.socket) (No such file or directory)
[ 24.296] (WW) Warning, couldn't open module intel
[ 24.296] (EE) Failed to load module "intel" (module does not exist, 0)
[ 24.318] (WW) Warning, couldn't open module nv
[ 24.318] (EE) Failed to load module "nv" (module does not exist, 0)
[ 24.318] (WW) Warning, couldn't open module fbdev
[ 24.318] (EE) Failed to load module "fbdev" (module does not exist, 0)
[ 24.319] (WW) Warning, couldn't open module vesa
[ 24.319] (EE) Failed to load module "vesa" (module does not exist, 0)
[ 24.351] (WW) Falling back to old probe method for modesetting
如何使用 nvidia 作为我的默认显卡？如果相关的话，我使用 xfce 作为我的桌面。