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

Michel Dänzer michel at daenzer.net
Fri Jul 18 18:15:57 PDT 2014

On 19.07.2014 00:47, Christian König wrote:
> Am 18.07.2014 05:07, 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.
> I've made a few tests today with the kernel part of the patches running
> Xonotic on Ultra in 1920 x 1080.
> Without any patches I get around ~47.0fps on average with my dedicated
> HD7870.
> Adding only "drm/radeon: Use write-combined CPU mappings of rings and
> IBs on >= SI" and that goes down to ~45.3fps.
> Adding on to off that "drm/radeon: Use VRAM for indirect buffers on >=
> SI" and the frame rate goes down to ~27.74fps.

Hmm, looks like I'll need to do more benchmarking of 3D workloads as well.

Alex, given those numbers, it's probably best if you remove the "Use
write-combined CPU mappings of rings and IBs on >= SI" change from your
tree as well for now.

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

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