Re: [PATCH 1/2] drm/i915: Remove use of the autoreported ringbuffer HEAD position

[Keith Packard <keithp@keithp.com>]

<#part sign=pgpmime>
On Wed, 8 Feb 2012 19:02:47 +0100, Daniel Vetter <daniel@ffwll.ch> wrote:

> The issue is that the first one introduces a pretty decent perf
> regression, iirc Chris mentions something much large than 10x slowdown
> on certain cairo traces on sna. So we can only merge the first one
> together with the second one.

Is there any effect on mesa or uxa?

> Yeah, that's kinda the issue which I've failed to phrase clearly in my mail ;-)

Frightening patches with that kind of global scope need a reason far
more compelling than a performance regression caused by a separate
correctness fix.

If we need the correctness patch to resolve a known problem (especially
a regression), then we'll take the performance hit and fix that in the
next release.

> Without this issue being confirmed on older machines I'm leaning
> towards merging both patches to -next - after all snb never really
> regressed because the offending commit changed behaviour from "dies as
> soon as the ring wraps" to "sometimes corrupts the ring".

If we don't see any significant issues in 'normal' usage (mesa and uxa),
then I agree, we should push both patches to -next.

-- 
keith.packard@intel.com