linux-kernel - Re: [PATCH] drm/i915: By default, enable RC6 on IVB and SNB when reasonable

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Date:	Wed, 23 Nov 2011 21:35:42 +0100
From:	Daniel Vetter <daniel@...ll.ch>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Daniel Vetter <daniel@...ll.ch>, rajesh.sankaran@...el.com,
	Keith Packard <keithp@...thp.com>,
	Matthew Garrett <mjg@...hat.com>,
	intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm/i915: By default, enable RC6 on IVB and SNB when
 reasonable

On Wed, Nov 23, 2011 at 03:43:05PM +0000, David Woodhouse wrote:
> On Wed, 2011-11-23 at 16:41 +0100, Daniel Vetter wrote:
> > Hm, that comment confuses me a bit. I've always thought that igfx_off only
> > instantiates a identity mapping and leaves the dmar unit on. Is that
> > wrong? 
> 
> It's completely off. If a DMAR unit has *only* graphics devices behind
> it (as the one for the built-in graphics does, because it's a whole
> boatload of speshul case for integration with the GTT), we just don't
> enable it at all. See the second for_each_drhd_unit() loop in
> init_no_remapping_devices().

That explanation confused me even more. So I've rechecked with
intel_iommu=igfx_off and already thought I've made a decent fool of
myself because I couldn't readily hang it. Turns out it's just much harder
to hang with that. So I think moving around the tlb flushing for other
dmar nodes to align with the idled igfx isn't a great solution, simply
because I can't reliably tell whether it fixes anything.
-Daniel
-- 
Daniel Vetter
Mail: daniel@...ll.ch
Mobile: +41 (0)79 365 57 48
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