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

[Jesse Barnes]

On Thu, 23 Jun 2011 21:08:02 +0100
Chris Wilson <chris at chris-wilson.co.uk> wrote:

> On Thu, 23 Jun 2011 10:11:26 -0700, Jesse Barnes <jbarnes at virtuousgeek.org> wrote:
> > I tested again and things were working as expected.  This patch adds a
> > debugfs file for dumping the ring freq table, can you guys test it out
> > (try disabling the call to update the table, dump it, make sure it's 0,
> > then re-enable and make sure it's programmed correctly).
> 
> According to the debugfs, your defaults should be effective:
> 
> sandybridge:~$ cat /sys/kernel/debug/dri/1/i915_ring_freq_table 
> GPU freq	Effective CPU freq
> 850		0 -> 1600
> 900		0 -> 1700
> 950		0 -> 1800
> 1000		0 -> 1800
> 1050		0 -> 1900
> 1100		0 -> 2000
> 
> I'll give the tyres another kick and see if I can spot any differences.

Eric was seeing an increase, but not as large as expected or hoped
for.  He saw a greater increase in performance than this patch provides
by simply keeping the CPU busy during his benchmark.  That could be due
to additional ring frequency when the CPU is in a turbo mode.  You may
be able to approach that by making the effective CPU frequency much
higher (maybe going up to 4GHz).

-- 
Jesse Barnes, Intel Open Source Technology Center