[Intel-gfx] gem clflush optimization for media encoding

[Keith Packard]

On Wed, 22 Jun 2011 12:29:21 +0800, "Zou, Nanhai" <nanhai.zou at intel.com> wrote:

>   As I understand,
>   with movnti + sfence, data should be surly reach memory. Cache should be coherent at this case.

I wouldn't mind seeing additional experiments in this area, but when
Eric and I tried this a couple of years ago, we found that without
clflush, data would not reliably be forced out to memory.
> 

> 	map_gtt in current gem is super slow. 
> 	I've tried map_gtt but it seems that the speed is unacceptable.

You almost certainly want to allocate a couple of sufficient GTT mapped
buffers and hang onto them; you'll call map_gtt only at startup, then
re-use the buffers.

>   A fast map_gtt implementation could be the best choice here.

Chris Wilson may have some ideas about how to speed up map_gtt, but I
suspect the best plan is to not need to speed it up by re-using the same
mapped buffers.

-- 
keith.packard at intel.com
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