[PATCH 1/6] DownloadFromScreenCS: download via a scratch BO if pixmap domain is unknown

[xmail at karlt.net]

Michel Dänzer writes:

> On Mit, 2010-09-01 at 10:39 +1200, Karl Tomlinson wrote: 

>> Again, the consequences of a CPU read from VRAM are much worse, I
>> expect/hope, than the consequences of GPU blit from GTT.  Maybe a
>> GPU blit when the BO is in CPU domain would be bad, but is it
>> likely to be busy in that situation?
>> 
>> I expect that the BO is usually in VRAM.  Pixmaps are created in
>> VRAM, UTS moves them to VRAM often enough, and most (or all) write
>> operations move them to VRAM.
>> 
>> I suspect the most likely time that the BO would not be in VRAM is
>> if it is has been evicted because it is not in use, and so the
>> choice doesn't matter (because it is not busy).
>
> FWIW, whether the BO is busy or not doesn't really matter for this. The
> code just uses radeon_bo_is_busy() for guessing where the BO might end
> up if it isn't referenced by the CS already.

I was using my words lazily, sorry.
By busy, I meant reserved.  I was considering that because that
is the situation where _bo_is_busy doesn't set the domain.

(FWIW, AIUI radeon_bo_is_busy returns [kind of] true when reserved.)