Created attachment 120852 [details]
xorg.log

System Environment: 
Regression: Yes     
Platform:  All the platforms(IVB/HSW/BYT/BSW/SKL)

Description:
When we run Gputest_v0.5_triangle_windows_640x480 case with bad test environment, we've found performance fps dropped by 12%.

And check 2D_X11perf_V1.5_aa10text and 2D_X11perf_V1.5_aa10text has more drop from 15%--60%. 

we try to do below steps to dig out which driver caused it:
1. compile good mesa/xf86/xserver onto the bad environment, performance fps still bad.
2. Switch to the good kernel on the bad environment, performance fps is bad 
3. Start gnome-session: performance is bad running with bad environment.
4. without start gnome-session: performance is good running with bad environment.
so seems like gnome-session related, we've no idea which driver impacted it.


Bad test environment:
Ubuntu 14.04 LTS
gnome-session 3.9.90
Kernel:4.4-rc8-drm-intel-nightly-0417da
Mesa: 86fa484
xf86: 2.99.917-523-g082a57e
xserver: 1.18.99.1


Good test environment:
Ubuntu 14.04 LTS
gnome-session 3.9.90
Kernel:4.4-rc6-drm-intel-nightly-ec0382
Mesa: dfce975
xf86: 2.99.917-517-gbc4ffba
xserver: 1.18.99.1

Reproduce steps:
1. xinit &
2. gnome-session &
3. ./GpuTest /test=triangle /width=640 /height=480 /fullscreen /benchmark /no_scorebox

xorg attached.