Plan: BO move throttling for visible VRAM evictions

[Marek Olšák]

On Fri, Apr 14, 2017 at 12:14 PM, Michel Dänzer <michel at daenzer.net> wrote:
> On 04/04/17 05:11 AM, Marek Olšák wrote:
>> On Fri, Mar 31, 2017 at 5:24 AM, Michel Dänzer <michel at daenzer.net> wrote:
>>> On 30/03/17 07:03 PM, Michel Dänzer wrote:
>>>> On 25/03/17 01:33 AM, Marek Olšák wrote:
>>>>> Hi,
>>>>>
>>>>> I'm sharing this idea here, because it's something that has been
>>>>> decreasing our performance a lot recently, for example:
>>>>> http://openbenchmarking.org/prospect/1703011-RI-RADEONDIR06/7b7668cfc109d1c3dc27e871c8aea71ca13f23fa
>>>>
>>>> The attached proof-of-concept patch (on top of Christian's "CPU mapping
>>>> of split VRAM buffers" series, ported from radeon) results in 145.05 fps
>>>> on my Tonga.
>>>
>>> I get the same result without my or Christian's patches though, with
>>> 4.11 based DRM or amd-staging-4.9. So I guess I just can't reproduce the
>>> problem with this test. Are there any other tests for it?
>>
>> It's random. Sometimes the benchmark runs OK, other times it's slow.
>> You can easily see the difference but observing how smooth it is. The
>> visible VRAM evictions result in constant 100-200ms stalls but not
>> every frame, which feels like the frame rate is much lower than it
>> actually is.
>>
>> Make sure your graphics details are maxed out. The best score I can
>> get with my rig is 70 fps. (Fiji & Core i5 3570)
>
> I'm getting around 53-54 fps at Ultra with Tonga, both with Mesa 13.0.6
> and Git.
>
> Have you tried if Christian's patches for CPU access to split VRAM
> buffers help? I can imagine that forcing contiguous VRAM buffers for CPU
> access could cause lots of other BOs to be unnecessarily evicted from
> VRAM, if at least one of their fragments happens to be in the CPU
> visible part of VRAM.

I've finally tested latest amd-staging-4.9 and I'm very pleased. For
the first time, the Deus Ex benchmark has almost no hiccups. I've
never seen it so smooth. At one point, the MB/s BO move rate increase
to 200MB/s, stayed there for a couple of seconds, and then it dropped
to 0 again. The frame rate was OK-ish, so I guess the moves didn't
happen all at once. I also tested DiRT Rally and I haven't been able
to reproduce the low FPS with the consistently-high BO move rate that
I saw several months ago.

We could do some move throttling there for sure, but it's much better
than it ever was.

Marek