[Intel-gfx] [PATCH v2 1/7] drm/i915/perf: rework aging tail workaround

[Lionel Landwerlin]

On 19/02/2019 09:18, Chris Wilson wrote:
> Quoting Lionel Landwerlin (2019-02-18 18:35:28)
>> We're about to introduce an options to open the perf stream, giving
>> the user ability to configure how often it wants the kernel to poll
>> the OA registers for available data.
>>
>> Right now the workaround against the OA tail pointer race condition
>> requires at least twice the internal kernel polling timer to make any
>> data available.
> I think this code is bogus. I do not think there is an aging problem on
> hsw+, the only cause of zeroes being written that I've found is from
> changing configs.
> -Chris
>

Hmm... I'm pretty sure there is an issue and it's actually worse on the 
HSW machine I have than on later machines.

The DRM_NOTE in that function is appearing a lot more on HSW.


Yes, there is also an issue with how long it takes to reprogram the GPU.


-Lionel