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 15:36:13 +0000
From:	David Woodhouse <dwmw2@...radead.org>
To:	Daniel Vetter <daniel@...ll.ch>
Cc:	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, 2011-11-23 at 16:31 +0100, Daniel Vetter wrote:
> 
> Things I've tried that don't work around the issue:
> - Disable dmar for the igfx with intel_iommu=igfx_off
> - Apply the ilk workaround (i.e. synchronous dmar tlb flushes + gpu
> idling while flushing).

Well, the ILK workaround was only ensuring that the gfx was idle while
the *graphics* IOTLB was flushed. We are still flushing the IOTLB for
*other* IOMMUs at arbitrary times. 

Might be interesting to go for *deferred* IOTLB flushes (i.e. the normal
mode without the workaround or 'intel_iommu=strict' on the command
line), *BUT* to make sure the batched flush (the flush_unmaps() call)
can *only* happen when the GPU is quiescent. You could do that with a
dirty hack for testing, and if *that* fixes the issue.... well, $DEITY
knows, someone still needs a good kicking, but at least we'll have
learned something :)

-- 
dwmw2

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