power usage increase by approx 4W between kernel 4.7.8 and 4.8.5

Submitted by bre..@..il.com

Assigned to Default DRI bug account

Link to original bug (#100270)

Description

Created attachment 130304
Log when booted under kernel 4.7.8

I'm running a cutdown Xfce Debian Stretch system on a Dell E6440 laptop. The laptop has an Intel 4th Gen and a Radeon HD 8670A/8670M/8690M / R5 M330 video device.

I've noticed an increase in power consumption between kernel 4.7.8 and kernel 4.8.5 of >4W.

Investigating further the increase seems to have been introduced between 4.8-rc2 and 4.8-rc3 (tested using binary mainline kernels from the Ubuntu Kernel PPA).

When booting between kernels, no changes are made to laptop config.

tlp is being used for power optimisation. tunables in powertop show the same optimisations under each kernel.

This was initially reported as a kernel bug (https://bugzilla.kernel.org/show_bug.cgi?id=193521). The response was "please file a bug report at freedesktop.org to get help from the graphics experts".

There is information attached to the kernel bug. I've also attached Xorg.O.log from running under kernel 4.7 and under kernel 4.9. I don't have 4.8.5 installed any longer but the problem remains under 4.9.13.

This is my first bug report, please advise any further info required.

Attachment 130304, "Log when booted under kernel 4.7.8":
Xorg.0.47.log