Massive power regression going 3.4->3.5

[James Bottomley]

On Wed, 2012-08-01 at 09:58 +0100, Chris Wilson wrote:
> On Wed, 01 Aug 2012 09:45:04 +0100, James Bottomley <James.Bottomley at HansenPartnership.com> wrote:
> > On Wed, 2012-08-01 at 09:16 +0100, Chris Wilson wrote:
> > > On Wed, 01 Aug 2012 09:06:12 +0100, James Bottomley <James.Bottomley at HansenPartnership.com> wrote:
> > > > I got the attached to apply and it doesn't really improve the idle power
> > > > much (12.5W).
> > > 
> > > That's good to know. Next step is to try overriding i915.semaphores.
> > > Can you please test with i915.semaphores=0 and i915.semaphores=1?
> > 
> > There's not much point doing i915_semaphores=1 since that's the default
> > on gen 6 hardware, but i915_semaphores=0 recovers and idle power of
> > ~6.5W
> 
> It is only the default if iommu is off, and changing the default
> was one of the side-effects of the patch you bisected.

Sandybridge mobile doesn't have an iommu (or at least, if it does, the
kernel doesn't detect it).

> Can you please login to the desktop, let it idle, record
> /sys/kernel/debug/dri/0/i915_cur_delayinfo and .../i915_drpc_info.
> Then trace-cmd record -e i915 sleep 10s, and follow up with a new pair
> of /sys/kernel/debug/dri/0/i915_cur_delayinfo and .../i915_drpc_info.
> 
> This will let us see whether the pm counters are truly advancing and
> what activity the driver is performing whilst idle.

With or without i915_semaphore=0?

James