Re: [PATCH 1/1] Revert "drm/i915: drop i915_ prefix from enable_rc6, enable_fbc, enable_ppgtt parameters"

[Amit Shah <amit.shah@redhat.com>]

On (Thu) 17 Jul 2014 [11:11:15], Daniel Vetter wrote:
> On Thu, Jul 17, 2014 at 02:32:41PM +0530, Amit Shah wrote:
> > On (Thu) 17 Jul 2014 [09:35:20], Daniel Vetter wrote:
> > > On Wed, Jul 16, 2014 at 9:54 PM, Linus Torvalds
> > > <torvalds@linux-foundation.org> wrote:
> > > > Sorry for the top post, I'm on the road..
> > > >
> > > > In wondering if we couldn't just keep both the old an the new names and have
> > > > them both point at the same variable? Remove the description for the old
> > > > name, but keep it working?
> > > 
> > > I'm really surprised here ... We have rc6 enabled by default
> > > everywhere, and all the additional rc6 levels that users try to enable
> > > are known to hard-hang machines.
> > 
> > I haven't had this problem on my hardware (ThinkPad T420s, lspci
> > below) for a few kernel versions.  I think I added the enable_rc6=
> > setting back from the time the deeper states were enabled and then
> > reverted for SandyBridge.
> > 
> > Nevertheless, with the current state, RC6p and RC6pp states are not
> > used.
> 
> Yeah, on snb they cause crashes and instability and also don't provide
> measurable power benefits (afaik). So I recommend you drop that one.

Not for me -- there have been no crashes / hangs / lockups as I
mentioned.

> > > I actually have plans to taint the
> > > kernel if you set any of them since I'm fed up with the random crash
> > > reports. Same for fbc, even more so or the ppgtt knob. My stance is
> > > that if you know about these knobs you _really_ should know the driver
> > > to its depths and so also be able to follow module parameter
> > > renamings.
> > 
> > I also remember there being bugzillas about power consumption, and
> > using this setting was recommended (for Fedora, I think).  I know
> > a few people are using this setting.
> 
> I know, google is littered with such entries. Unfortunately by the time
> google thinks something is important (which usually takes a few months)
> it's already badly outdated: i915 graphics developement is charging ahead
> at a really brisk pace - we merge a few hundred patches per release for
> i915 alone.

But for SNB, there's really no "improvement" for the RC6 states, is
there?

> > > > On Jul 16, 2014 8:34 AM, "Amit Shah" <amit.shah@redhat.com> wrote:
> > > >>
> > > >> This reverts commit 3adee7a7976012a20f1d3b5a529a3c105e29fef1.
> > > >>
> > > >> After upgrading to v3.15, my laptop's battery started draining quite
> > > >> fast.  Powertop pointed to the deep RC6 states not being used.  The
> > > >> kernel param I had put to enable them had stopped working the way it
> > > >> used to; so I disagree with the 'not maintaing ABI' part of the param
> > > >> name change.
> > > >>
> > > >> However weird the names may be, they're in active use and changing them
> > > >> only causes pain for users.  This also isn't advertised (marked
> > > >> deprecated, big warning shown, etc.), so just reverting now.
> > > >>
> > > >> CC: Daniel Vetter <daniel.vetter@ffwll.ch>
> > > >> CC: Jani Nikula <jani.nikula@linux.intel.com>
> > > >> CC: David Airlie <airlied@linux.ie>
> > > >> CC: <stable@vger.kernel.org> # v3.15+
> > > >> Signed-off-by: Amit Shah <amit.shah@redhat.com>
> > > 
> > > Anyway we need to figure out what went wrong here. Please share your
> > > exact kernelcmdline and lspci -nn. Also stats for before/after from
> > > powertop when idle please.
> > 
> > Powertop stats for idle are a little difficult -- since this is my
> > primary laptop.
> 
> Now I'm a bit confused: How have you measured that the lack of rc6p/pp is
> the reason for your power consumption regression?
> -Daniel

What I meant was rebooting in the middle of something is a pain
(usually a week or two between trying these things); and also for a
fair comparison, the workloads have to be similar for both the
powertop ratings.

In any case, my daily work doesn't change, and I noticed this
immediately upon booting into 3.15.  The laptop heats up a bit more,
that's the first clue; and the battery doesn't provide as much backup
as it used to.

		Amit