[PATCH 0/3] drm/amdgpu: Tweaks for high pressure on CPU visible VRAM

[Marek Olšák]

On Wed, May 24, 2017 at 9:56 AM, Michel Dänzer <michel at daenzer.net> wrote:
> On 23/05/17 07:38 PM, Marek Olšák wrote:
>> On Tue, May 23, 2017 at 2:45 AM, Michel Dänzer <michel at daenzer.net> wrote:
>>> On 22/05/17 07:09 PM, Marek Olšák wrote:
>>>> On Mon, May 22, 2017 at 12:00 PM, Michel Dänzer <michel at daenzer.net> wrote:
>>>>> On 20/05/17 06:26 PM, Marek Olšák wrote:
>>>>>> On May 20, 2017 3:26 AM, "Michel Dänzer" <michel at daenzer.net
>>>>>> <mailto:michel at daenzer.net>> wrote:
>>>>>>
>>>>>>     On 20/05/17 01:14 AM, Marek Olšák wrote:
>>>>>>     > Hi Michel,
>>>>>>     >
>>>>>>     > I've applied your series
>>>>>>
>>>>>>     Thanks for testing it.
>>>>>>
>>>>>>     > and it doesn't help with low Dirt Rally performance on Fiji. I see TTM
>>>>>>     > buffer moves at 800MB/s and many VRAM page faults.
>>>>>>
>>>>>>     Did you see this:
>>>>>>
>>>>>>     >> Note that there's only little if any improvement of the average
>>>>>>     framerate
>>>>>>     >> reported, but the minimum framerate as seen on the HUD goes from
>>>>>>     ~10 fps
>>>>>>     >> to ~17.
>>>>>>
>>>>>>     I.e. it mostly affects the minimum framerate and smoothness for me
>>>>>>     as well.
>>>>>>
>>>>>>
>>>>>> Without the series, I get 70 average fps. With the series, I get 30
>>>>>> average fps. That might just be random bad luck. I don't know.
>>>>>
>>>>> Hmm, yeah, maybe that was just one of the random slowdowns you've been
>>>>> talking about in other threads and on IRC?
>>>>>
>>>>> I can't reproduce any slowdown with these patches, even leaving visible
>>>>> VRAM size at 256 MB.
>>>>
>>>> The random slowdowns with Dirt Rally are only caused by the pressure
>>>> on visible VRAM. This whole thread is about those random slowdowns.
>>>
>>> No, this thread is about the scenario described in the cover letter of
>>> this patch series.
>>>
>>>
>>>> If you're saying "maybe it was just one of the random slowdowns", you're
>>>> saying "maybe it was just the visible VRAM pressure". It's only
>>>> random with Dirt Rally, which makes it difficult to believe statements
>>>> such as "I can't reproduce any slowdown".
>>>
>>> I could say the same thing about you seeing random slowdowns... I've
>>> never seen that, I had to artificially limit the size of visible VRAM to
>>> 64 MB to make it significantly affect the benchmark result.
>>>
>>> How many times do you need to run the benchmark on average to hit a
>>> random slowdown? Which desktop environment and other X clients are
>>> running during the benchmark? Which tab is active in the Steam window
>>> while the benchmark runs?
>>>
>>> In my case, it's only xfwm4, xterm and steam on the Dirt Rally page in
>>> the library.
>>
>> Ubuntu Unity, Steam small mode (there are no tabs), Ultra settings in
>> Dirt Rally.
>>
>> Every single time I run the game with this series, I get 700-1000MB/s
>> of TTM BO moves. There doesn't seem to be any randomness.
>>
>> It was better without this series. (meaning it was sometimes OK, sometimes bad)
>
> Thanks for the additional details. I presume that in the bad case there
> are some BOs lying around in visible VRAM (e.g. from Unity), which
> causes some of Dirt Rally's BOs to go back and forth between GTT on CPU
> page faults and VRAM on GPU usage.
>
> This means at least patch 2 goes out the window. I'll see if I can
> salvage something out of patch 3.

I think the final solution (done in fault_reserve_notify) should be:
if (bo->num_cpu_page_faults++ > 20)
   bo->preferred_domain = GTT_WC;

Otherwise I think we'll be just going in circles and not get anywhere.

Marek