Long radeon stalls on recent kernels

[Andy Lutomirski]

On Wed, Dec 10, 2014 at 1:44 AM, Michel Dänzer <michel at daenzer.net> wrote:
> On 10.12.2014 06:39, Andy Lutomirski wrote:
>> On Tue, Dec 9, 2014 at 8:06 AM, Andy Lutomirski <luto at amacapital.net> wrote:
>>> On Tue, Dec 9, 2014 at 1:18 AM, Michel Dänzer <michel at daenzer.net> wrote:
>>>> On 09.12.2014 09:24, Andy Lutomirski wrote:
>>>>>
>>>>> The relevant line from latencytop seems to be:
>>>>>
>>>>> 154 20441402 489139 radeon_fence_default_wait [radeon]
>>>>> fence_wait_timeout ttm_bo_wait [ttm] ttm_bo_move_accel_cleanup [ttm]
>>>>> radeon_move_blit.isra.12 [radeon] radeon_bo_move [radeon]
>>>>> ttm_bo_handle_move_mem [ttm] ttm_bo_evict [ttm] ttm_mem_evict_first
>>>>> [ttm] ttm_bo_mem_space [ttm] ttm_bo_validate [ttm]
>>>>> radeon_bo_fault_reserve_notify [radeon]
>>>>
>>>> Which process is this?
>>>
>>> Xorg
>>>
>>>>
>>>> Looks like CPU access to a BO in VRAM, but the BO is located outside of
>>>> the CPU visible area of VRAM, so it has to be moved into the CPU visible
>>>> area first.
>>>>
>>>> Which version of Mesa are you using?
>>>>
>>>
>>> mesa-dri-drivers-10.3.3-1.20141110.fc20.x86_64
>>>
>>> I'm planning on upgrading to Fedora 21 fairly soon.
>>
>> Upgrading to mesa-dri-drivers-10.3.3-1.20141110.fc21.x86_64 seems to
>> have helped enough that my usual test (open a couple of Firefox tabs
>> with graphics in them) doesn't hang anymore.
>
> Hmm, since that looks like the exact same upstream version, maybe it was
> actually upgrading something else that made the difference?
>

Maybe mutter?

>
>> This card still isn't *fast*.
>
> I'm afraid it wasn't exactly a high-end card even when it was new. What
> kind of operations are slow?

Things like scrolling in Google Maps.  It's not *that* bad, but older
Intel IGPs still seem considerably smoother.

>
>
>> Is there some way I can check that I'm actually using all 16 PCIe lanes?
>> In my tinkering w/ power management settings, I got some odd logs
>> suggesting that only one lane was in use.
>
> You can try forcing off ASPM with radeon.aspm=0, other than that I'm not
> sure.
>
>
>> But I'm still waiting for the day that buggy userspace *can't* cause
>> kernel graphics stalls.
>
> Actually, this looks more like buggy userspace stalling itself. :)

I thought the stall was the kernel evicting things from vram.  Why
does it need to wait for userspace for that?  Is it that userspace is
actively using whatever's being evicted?

--Andy

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



-- 
Andy Lutomirski
AMA Capital Management, LLC