[Intel-gfx] [PATCH 2/2] drm/i915: re-enable rc6 by default

[Daniel Vetter]

On Wed, Nov 16, 2011 at 16:59, Andrew Lutomirski <andy at luto.us> wrote:
>
> On Nov 16, 2011 7:54 AM, "Daniel Vetter" <daniel.vetter at ffwll.ch> wrote:
>>
>> On Mon, Nov 14, 2011 at 21:39, Eugeni Dodonov <eugeni.dodonov at intel.com>
>> wrote:
>> > Most of the rc6-related hangs and major issues were addressed for the
>> > past
>> > months.
>> >
>> > Let's re-enable it by default to provide a more wider testing, and catch
>> > the remaining problems.
>> >
>> > According to tests, enablement of rc6 results in up to +50% improvements
>> > in power usage and battery life, so it certainly would be a nice feature
>> > to have enabled by default.
>> >
>> > Also, most of the issues related to rc6 seem to came from VTd, so if you
>> > are experiencing any problems with it, try disabling VTd in bios or
>> > using
>> > intel_iommu=off kernel parameter to investigate whether it solves the
>> > issue.
>> >
>> > Acked-by: Keith Packard <keithp at keithp.com>
>> > CC: Daniel Vetter <daniel.vetter at ffwll.ch>
>> > CC: Jesse Barnes <jbarnes at virtuousgeek.org>
>> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=38567
>> > Signed-off-by: Eugeni Dodonov <eugeni.dodonov at intel.com>
>>
>> Iirc the same applies to rc6 as to semaphores. We have bug reports
>> that it causes hard-hangs in combination with DMAR. I haven't yet
>> gotten around to poking the relevant reporters whether ppgtt changes
>> anything, because internet access here at the Intel Poland site sucks.
>> So again I think we need to disable this on snb when DMAR is on.
>
> I can reproduce the semaphore hang easily.  Where are the ppgtt
> patches/settings to play with?
>
> FWIW, rc6 is a *huge* win on my SNB laptop, and the laptop has always been
> rock-solid with any set of options.  Maybe this is only an issue on desktop
> parts, and the 5W difference is a bigger deal on laptops anyway.

Grab the ppgtt branch from my fdo repo:

http://cgit.freedesktop.org/~danvet/drm/

Note that this branch will only work on snb/ivb and that resume is
broken. Also, after the first gpu reset ppgtt will get disabled and
hence your machine might die rather quickly. So perhaps boot with
i915.reset=0 to prevent that.

Testing feedback highly welcome.

Yours, Daniel
-- 
Daniel Vetter
daniel.vetter at ffwll.ch - +41 (0) 79 365 57 48 - http://blog.ffwll.ch