Am 28.03.2017 um 10:35 schrieb Michel Dänzer:
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.
Yeah, John and I are already working on this (but mostly for GFX9).
The difference is that VRAM allocations are mostly contiguously, while
GTT allocations are scattered. So you got more TLB pressure with GTT.
Christian.
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