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

[Michel Dänzer]

On 25/05/17 08:24 PM, Marek Olšák wrote:
> On Thu, May 25, 2017 at 5:31 AM, Michel Dänzer <michel at daenzer.net> wrote:
>> On 24/05/17 08:27 PM, Christian König wrote:
>>> Am 24.05.2017 um 13:03 schrieb Marek Olšák:
>>>>>
>>>> I think the final solution (done in fault_reserve_notify) should be:
>>>> if (bo->num_cpu_page_faults++ > 20)
>>>>     bo->preferred_domain = GTT_WC;
>>
>> I agree something like that will probably be part of the solution, but I
>> doubt it's quite that simple or that it's the only thing that can be
>> improved.
>>
>>
>>> I more or less agree on that, but setting preferred_domain permanently
>>> to GTT_WC is what worries me a bit.
>>>
>>> E.g. imagine you alt+tab from a game to your browser and back and the
>>> game runs way slower now because BOs are never moved back to VRAM.
>>
>> Right, permanently moving a BO to GTT might itself cause performance to
>> drop down a cliff in some cases. It's possible that this is irrelevant
>> compared to excessive buffer migration for CPU access though.
>>
>>
>>> What we need is a global limit of number of bytes transfered per second
>>> for swap operations or something like that.
>>>
>>> Or maybe a timeout which says when a BO was moved (either by swapping it
>>> out or by a CPU page fault) only move it back after +n jiffies or
>>> something like that.
>>
>> I also feel like something like this will be more useful than the number
>> of CPU page faults per se. But I'm curious what Marek comes up with. :)
> 
> I don't have any better idea at the moment. It looks like John Brooks
> has already solved this issue based on his IRC comments.

I don't think there's "the issue" with a single solution. None of John's
patches that I've tried so far help for the scenario described in the
cover letter of this series.


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