[Intel-gfx] [PATCH] drm/i915: Remove temporary allocation of dma addresses when rotating

[Chris Wilson]

On Mon, Feb 27, 2017 at 09:55:10AM +0000, Tvrtko Ursulin wrote:
> 
> On 22/02/2017 08:44, Chris Wilson wrote:
> >I also think that's an argument for improving the general cache rather
> >than arguing against using it.
> 
> Well I wasn't concerned about the cache per se, but about whether it
> is completely appropriate (best choice) to use it in this particular
> case.
> 
> Because as I said before, for 1920x1080x32 we are talking about a
> 16KiB extremely short lived temporary allocation, vs the similar
> size for the sg radix cache. But radix cache sticks around the the
> lifetime of obj->mm.pages and it wouldn't otherwise be there since
> AFAICS in practice no one really touches frame buffers in a way to
> trigger its creation.
> 
> Those amounts of memory are not a concern, but again, is the
> simplification of the code worth the conceptual downsides mentioned
> above? Even if we considered 4K frame buffers, when both allocations
> go to ~64KiB, would that change anything? I am not sure, probably
> not for me.
> 
> So I am still unsure that we should go with this change.

Again, the complaint you have here are general concerns about caching
the mapping. Avoiding using the cache instead of improving the cache
seems the wrong approach.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre