[Intel-gfx] [PATCH 2/2] drm/i915: enable plain RC6 on Sandy Bridge by default

Eugeni Dodonov eugeni at dodonov.net
Mon Feb 13 01:34:48 CET 2012

On Sun, Feb 12, 2012 at 18:10, Keith Packard <keithp at keithp.com> wrote:

> <#part sign=pgpmime>
> On Sat, 11 Feb 2012 17:24:16 -0200, Eugeni Dodonov <eugeni at dodonov.net>
> wrote:
> > So far I had 2 reports saying that RC6 solved the problems which were
> > present with RC6+RC6p (previous default) on SNB.
> For -fixes, I think we shouldn't enable rc6 by default, but we may want
> to change what enabling rc6 does on SNB to stop using deeper states?
> That should let more people enable it manually at least.

Hi Keith,

what if we pick only the 1st patch in this series for -fixes? It won't
change the defaults in any way, but it will allow the ones willing to
enable it manually on SNB to prevent issues.

E.g., with this patch, passing i915_enable_rc6=1 will enable plain RC6, and
leave deep RC6 off. This is probably the safest setting so far - it results
in nice power savings and all the other benefits of RC6, but avoid entering
RC6+ - which seems to be responsible for all the issues on the affected
machines apparently. And it would further help to isolate which rc6 states
are the guilty ones on the affected machines, so in case any other problem
arises, we can ask people to test with different 'i915_enable_rc6=N'
parameter prior to fully reverting it again..

The change of the default value for SNB could go into -next kernel. By the
time we'll get to the first release of 3.4 we'll certainly know if there
are any issues with that.

Eugeni Dodonov
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