[Intel-gfx] [PATCH] drm/i915/tgl: WaDisableGPGPUMidThreadPreemption

[Ye, Tony]

On 3/5/2020 1:01 AM, Rafael Antognolli wrote:
> On Wed, Mar 04, 2020 at 04:24:13PM +0000, Tvrtko Ursulin wrote:
>>
>> On 04/03/2020 16:02, Rafael Antognolli wrote:
>>> On Wed, Mar 04, 2020 at 03:31:44PM +0000, Tvrtko Ursulin wrote:
>>>> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>>>>
>>>> Enable FtrPerCtxtPreemptionGranularityControl bit and select thread-
>>>> group as the default preemption level.
>>>>
>>>> v2:
>>>>    * Remove register whitelisting (Rafael, Tony).
>>>>
>>>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>>>> Cc: Michał Winiarski <michal.winiarski at intel.com>
>>>> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
>>>> Cc: piotr.zdunowski at intel.com
>>>> Cc: michal.mrozek at intel.com
>>>> Cc: Tony Ye <tony.ye at intel.com>
>>>> Cc: Rafael Antognolli <rafael.antognolli at intel.com>
>>>
>>> Thanks for CC'ing me. I also saw a reply from Jason yesterday, but I
>>> don't see it in the list now (though my mail client a mess lately).
>>
>> I saw nothing from Jason, but there was an email from you asking about
>> interface descriptors and whitelisting which is why I copied you.
>>
>>> But he asked whether it's possible for Media and OpenCL drivers to
>>> also disable mid-thread preemption through the
>>> INTERFACE_DESCRIPTOR_DATA, instead of from the kernel side, so we could
>>> try to experiment with it in the future.
>>>
>>> Also, do you have an idea of how broken it is? Or is it just not tested
>>> because no driver is currently implementing it? And do you know if the
>>> windows 3D drivers implement it at all? I see code in the driver that
>>> seems to me that it's only disabled in certain cases...
>>>
>>> To summarize, I think we should either:
>>>      1) Disable mid-thread preemption from the kernel and not whitelist
>>>      the register (just like you do in this patch); or
>>>      2) Not do anything at all from the kernel, and let userspace disable
>>>      it if needed.
>>>
>>> I think 2) is better, if it's not an issue to the other userspace
>>> drivers (OpenCL and Media).
>>
>> I know it is somewhat broken like in
>> https://gitlab.freedesktop.org/drm/intel/issues/1293.
>>
>> And I know OpenCL and Media would prefer i915 to handle it, but that's
>> always the case. :) OpenCL and Media folks are on the thread so can comment
>> if they are okay with handling this themselves.
>>
>> Indeed a blanket ban in i915 means no one can try it out later without
>> further kernel changes.
> 
> Well, based on your comment from the previous patch:
> 
> "General thinking is, since MTP is considered not validated / broken /
> dangerous, i915 should default it off. But yes, whitelisting or not on
> top is open."
> 
> Maybe we should simply ban it and be done. So this patch is:
> 
> Acked-by: Rafael Antognolli <rafael.antognolli at intel.com>

Acked-by: Tony Ye <tony.ye at intel.com>

> 
>> Regards,
>>
>> Tvrtko