Gala high cpu usage with nvidia drivers

[Martin Hansen]

I have a Dell M3800 pc with Intel 4600 graphics card as well as a Nvidia Quadro K1100M graphics card.

I have installed on the same pc 2 versions of elementary OS (freya) for testing reasons. In one of the installations I am using the nouveau driver. Here I am able to do things like expose windows (Super+W) several times and all I get is 5% CPU usage from gala.

In the other setup I have NVIDIA driver installed (have tried several versions, same problem) and when I do Super+W there I get huge spikes in gala cpu usage, 80-100%.

When I try to run games in the two setups, like half life deathmatch, it runs very good with the nvidia driver (4k resolution, 60fps-ish, all on max) and good performance with the nouveau driver (4k, 40fps ish, all max ).

So it seems the nvidia driver is installed correctly since I get so good performance in games with it.

But in gala not so much. Well The animation of super+w is good, but chewing a lot of cpu.

The nvidia card is not attached to the screen directly but requires the intel card to display the output:

lspci | egrep "VGA|3D"
00:02.0 VGA compatible controller: Intel Corporation 4th Gen Core Processor Integrated Graphics Controller (rev 06)
02:00.0 3D controller: NVIDIA Corporation GK107GLM [Quadro K1100M] (rev a1)

This means I have this xorg.conf file:

Section "ServerLayout"
    Identifier "layout"
    Screen 0 "nvidia"
    Inactive "intel"
EndSection

Section "Device"
    Identifier "intel"
    Driver "intel"
    BusID "PCI:0@0:2:0"
    Option "AccelMethod" "SNA"
EndSection

Section "Screen"
    Identifier "intel"
    Device "intel"
EndSection

Section "Device"
    Identifier "nvidia"
    Driver "nvidia"
    BusID "PCI:2@0:0:0"
    Option "ConstrainCursor" "off"
EndSection

Section "Screen"
    Identifier "nvidia"
    Device "nvidia"
    Option "AllowEmptyInitialConfiguration" "on"
    Option "IgnoreDisplayDevices" "CRT"
EndSection

I have noticed something weird (i think)
When running glxgears with vblank_mode=0 I get around 450 with the nvidia setup but around 5000 using nouveau.
However when I move another window in front of the window with the gears (so that I cannot see the animation) I get a huge spike with the nvidia setup. Almost 30 times more, over 11200 vs 400 earlier.

When doing the same with the nouveau setup, I get no noticeable difference (which is expected right?)

Since I get so good performance in games, this leads me to think there is a problem in gala or a related program.

Any help is appreciated.