[RFC] drm/ttm: add minimum residency constraint for bo eviction

[Jerome Glisse]

On Wed, Nov 28, 2012 at 4:51 PM, Marek Olšák <maraeo at gmail.com> wrote:
> I think the problem with Radeon/TTM is much deeper. Let me demonstrate
> it on the following example.
>
> Unigine Heaven needs about 385MB of space for static resources, that's
> only 75% of my 512MB card. Yet, TTM is not capable of getting all of
> that into VRAM. If I allow GTT placements, I get 20 fps, which is the
> old Mesa behavior. If I force VRAM placements, I get 3 fps, because we
> validate buffers 10 times per frame and there's probably a lot of
> buffer evictions during each validation.
>
> In theory, we should get the best performance if Radeon/TTM managed to
> get everything into VRAM. That's what fglrx probably does. 75% of VRAM
> doesn't look like too much. And that's the problem. Even if we
> seemingly have enough memory, the current stack is not capable of
> using it efficiently.
>
> Marek
>

If you read my second to last paragraph this is what i explain. Right
now it inefficient because each cs try to revalidate things and thus
trigger bo move which increase fragmentation of memory at each cs. As
i explain a way better solution is to have a true heuristic in bo
placement and to not revalidate in different location things at each
cs. I was working on something like that, but the minimum residency
time just fix most of the regression and is a lot simpler and lot
smaller patch so i consider it as a temporary fix and i also believe
that in itself it make sense by putting some boundary on buffer move
frequency.

Cheers,
Jerome