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

Michel Dänzer michel at daenzer.net
Wed May 24 07:56:19 UTC 2017

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.

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

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