[Intel-gfx] [PATCH] drm/i915: initialize ring frequency scaling table on SNB

[Jesse Barnes]

On Wed, 22 Jun 2011 11:42:04 -0700
Eric Anholt <eric at anholt.net> wrote:

> On Tue, 21 Jun 2011 15:24:24 -0700, Jesse Barnes <jbarnes at virtuousgeek.org> wrote:
> > The ring frequency scaling table tells the PCU to treat certain GPU
> > frequencies as if they were a given CPU frequency for purposes of
> > scaling the ring frequency.  Normally the PCU will scale the ring
> > frequency based on the CPU P-state, but with the table present, it will
> > also take the GPU frequency into account.  The scaling_factor used in
> > this patch may not be ideal, but is enough to increase performance in
> > nexuiz on a 1366x768 panel by about 20%.
> > 
> > The main downside of keeping the ring frequency high while the CPU is
> > at a low frequency (or asleep altogether) is increased power
> > consumption.  But then if you're keeping your GPU busy, you probably
> > want the extra performance.
> 
> The intent of the patch sounds good, but it doesn't seem to be doing
> anything here (graphs below).  If I run a "while true; do; done" loop to
> keep a CPU busy during measurement, though, OA gets a 15.9% +/- 0.6%
> win, and nexuiz around 20%.  There are no complaints in dmesg.

Ok I'll checck it out; I admit I tested it then made a few changes then
sent it out, so I must have broken something...

Jesse