[Intel-gfx] [PATCH 7/7] drm/i915: Allow user to set cache at BO creation

[Yang, Fei]

>Subject: Re: [Intel-gfx] [PATCH 7/7] drm/i915: Allow user to set cache at BO creation
>
>On 04/04/2023 19:04, Yang, Fei wrote:
>>> Subject: Re: [Intel-gfx] [PATCH 7/7] drm/i915: Allow user to set
>>> cache at BO creation
>>>
>>> On 01/04/2023 09:38, fei.yang at intel.com wrote:
>>>> From: Fei Yang <fei.yang at intel.com>
>>>>
>>>> To comply with the design that buffer objects shall have immutable
>>>> cache setting through out its life cycle, {set, get}_caching ioctl's
>>>> are no longer supported from MTL onward. With that change caching
>>>> policy can only be set at object creation time. The current code
>>>> applies a default (platform dependent) cache setting for all objects.
>>>> However this is not optimal for performance tuning. The patch
>>>> extends the existing gem_create uAPI to let user set PAT index for
>>>> the object at creation time.
>>>> The new extension is platform independent, so UMD's can switch to
>>>> using this extension for older platforms as well, while {set,
>>>> get}_caching are still supported on these legacy paltforms for
>>>> compatibility reason.
>>>>
>>>> Cc: Chris Wilson <chris.p.wilson at linux.intel.com>
>>>> Cc: Matt Roper <matthew.d.roper at intel.com>
>>>> Signed-off-by: Fei Yang <fei.yang at intel.com>
>>>> Reviewed-by: Andi Shyti <andi.shyti at linux.intel.com>
>>>
>>> Just like the protected content uAPI, there is no way for userspace
>>> to tell this feature is available other than trying using it.
>>>
>>> Given the issues with protected content, is it not thing we could want to add?
>> Sorry I'm not aware of the issues with protected content, could you elaborate?
>> There was a long discussion on teams uAPI channel, could you comment
>> there if any concerns?
>>
>> https://teams.microsoft.com/l/message/19:f1767bda6734476ba0a9c7d147b92
>> 8d1 at thread.skype/1675860924675?tenantId=46c98d88-e344-4ed4-8496-4ed771
>> 2e255d&groupId=379f3ae1-d138-4205-bb65-d4c7d38cb481&parentMessageId=16
>> 75860924675&teamName=GSE%20OSGC&channelName=i915%20uAPI%20changes&crea
>> tedTime=1675860924675&allowXTenantAccess=false
>>
>> Thanks,
>> -Fei
>
>
> We wanted to have a getparam to detect protected support and were told
> to detect it by trying to create a context with it.
>
> Now it appears trying to create a protected context can block for several
> seconds.
>
> Since we have to report capabilities to the user even before it creates
> protected contexts, any app is at risk of blocking.

Can we detect this capability by creating a buffer object? This extension is
not blocking, it just provide a way to set caching policy, and should complete
very fast. There is a IGT test I created for this extension (not merged yet),
please take a look at http://intel-gfx-pw.fi.intel.com/series/19149/

I'm not familiar with getparam, will take a look there as well. But I think it
would be easier just create an object.

-Fei

>-Lionel
>
>
>>
>>> Thanks,
>>>
>>> -Lionel
>>>
>>>
>>>> ---
>>>>    drivers/gpu/drm/i915/gem/i915_gem_create.c | 33 ++++++++++++++++++++
>>>>    include/uapi/drm/i915_drm.h                | 36 ++++++++++++++++++++++
>>>>    tools/include/uapi/drm/i915_drm.h          | 36 ++++++++++++++++++++++
>>>>    3 files changed, 105 insertions(+)
>>>>