Plan: BO move throttling for visible VRAM evictions

Michel Dänzer michel at
Tue Mar 28 08:35:26 UTC 2017

On 28/03/17 05:29 PM, Christian König wrote:
> Am 28.03.2017 um 08:00 schrieb Michel Dänzer:
>> On 28/03/17 12:50 PM, zhoucm1 wrote:
>>> On 2017年03月28日 10:40, Michel Dänzer wrote:
>>>> On 27/03/17 04:53 PM, Zhou, David(ChunMing) wrote:
>>>>> For APU special case, can we prevent eviction happening between VRAM
>>>>> <----> GTT?
>>>> We can, if we can close the performance gap between VRAM and GTT. We
>>>> measured around 30% gap a while ago, though right now I'm only
>>>> measuring
>>>> ~5%, but the test system has slower RAM now (still dual channel
>>>> though).
>>> My impression VRAM and GTT have no much difference for APU case, if I'm
>>> wrong, pls correct me.
>> The Mesa patch below makes radeonsi use mostly GTT instead of mostly
>> VRAM, and slows down Unigine Valley by about 5% on my desktop Kaveri.
>> You can try it for yourself.
> Additional to that you still need the stolen VRAM on APUs for page
> tables and DCE.
> So we need to keep the eviction from VRAM to GTT enabled, but what we
> don't do is swapping them back in because Marek added the GTT flags on
> APUs as extra domain to look into.

As long as there's a performance gap between VRAM and GTT, this means
that performance of long-running apps (e.g. Xorg or the compositor) will
degrade over time, or after e.g. a suspend-resume cycle.

OTOH, if we can close the gap, we can stop trying to put most BOs in
VRAM in the first place with APUs.

Earthling Michel Dänzer               |     
Libre software enthusiast             |             Mesa and X developer

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