[PATCH 0/5] radeon: Write-combined CPU mappings of BOs in GTT

[Michel Dänzer]

On 18.07.2014 12:58, Dieter Nützel wrote:
> Am 18.07.2014 05:07, schrieb Michel Dänzer:
>> On 17.07.2014 19:09, Christian König wrote:
>>> Am 17.07.2014 12:01, schrieb Michel Dänzer:
>>>> [PATCH 5/5] drm/radeon: Use VRAM for indirect buffers on >= SI
>>>
>>> I'm still not very keen with this change since I still don't understand
>>> the reason why it's faster than with GTT. Definitely needs more testing
>>> on a wider range of systems.
>>
>> Sure. If anyone wants to give this patch a spin and see if they can
>> measure any performance difference, good or bad, that would be
>> interesting.
>>
>>> Maybe limit it to APUs for now?
>>
>> But IIRC, CPU writes to VRAM vs. write-combined GTT are actually an even
>> bigger win with dedicated GPUs than with the Kaveri built-in GPU on my
>> system. I suspect it may depend on the bandwidth available for PCIe vs.
>> system memory though.
> 
> Michel,
> 
> please, please do NOT change anything on this!;-)
> You all know that I currently can only run this on my poor Duron 1800
> with RV730 (AGP), but...
> 
> With this all 'objview' demos (mesa-demos) run at 60 fps (vsync),
> even with chip set/CPU power management enabled (athcool on).
> 
> If I set vblank_mode=0
> the slowest GreatLakesBiplaneHP.obj
> run at ~100 fps (~16 fps before) => 6x speedup.
> (Even 5 planes run at 30 fps) - Wow!!!

That's great, but note that the disputed change above only has an effect
with SI or newer GPUs, i.e. none with yours.

I suspect that speedup is because the app ends up using effectively
static vertex/index buffers, which are now in VRAM instead of in GTT due
to my Mesa changes.


> Overall X/Kwin eXperience is much better.
> Let me know which benchmarks you need.

I'm not looking for anything in particular, basically anything where you
care about performance. E.g. the usual suspects in PTS.


> BTW Do anyone know how I can override BIOS GTT settings?
> I can only set 256 MB max. - BIOS patching?

Your AGP bridge hardware might not support more.

> With agpmode=-1 I can run with 1024 MB GTT

What effect does that have on performance? I'm not sure if AGP provides
any benefit for GPUs with PCIe GART.


-- 
Earthling Michel Dänzer            |                  http://www.amd.com
Libre software enthusiast          |                Mesa and X developer