I got fed up with my 945gm not being capabile of 60fps glxgears.
commit d938da6b132a2d6addeba4c57a67ec3c07824843
Author: Ville Syrjälä <ville.syrj...@linux.intel.com>
Date: Fri Mar 22 20:08:03 2019 +0200
drm/i915: Disable C3 when enabling vblank interrupts on i945gm
The main difference compared to the older pm_qos attempts is that I
found a way to dig out the exact c3 disable latency, so we should have a
reasonable guarantee that we do disable c3 but not c2. The power cost of
not using c3 seems to be about 0.7W on my machine (with the display on),
so this isn't exactly cheap :(
I did spend quite a bit of time at some point digging through the
chipset docs (such as they are). It's been a while since I did that but
I'll try to summarize what I recall; Gen3 introduced some kind of new
mechanism by which the gmch can wake up the CPU. The old AGPBUSY/PM_BUSY
involved the ICH as well IIRC, whereas the new mechanism supposedly does
not. IIRC the new mechanism already appears in the i915gm docs, but my
theory is that i945gm is where it actually got into use and either it is
broken or we're missing some magic undocumented bit somewhere. I did try
(blindly if necessary) poking at various registers that seemed relevant.
Alas, I was unable to find a magic bit to make C3+vblank interrupts
cooperate.
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https://bugs.launchpad.net/bugs/1087582
Title:
[gen3] Bad GPU performance whilst CPU is in deep sleep
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