[Intel-xe] [PATCH 01/10] drm/xe/oa: Introduce OA uapi

[Umesh Nerlige Ramappa]

On Tue, Aug 15, 2023 at 06:30:12PM -0700, Dixit, Ashutosh wrote:
>On Tue, 15 Aug 2023 18:11:55 -0700, Umesh Nerlige Ramappa wrote:
>>
>> >> +	/**
>> >> +	 * Multiple engines may be mapped to the same OA unit. The OA unit is
>> >> +	 * identified by class:instance of any engine mapped to it.
>> >> +	 *
>> >> +	 * This parameter specifies the engine class and must be passed along
>> >> +	 * with DRM_XE_OA_PROP_OA_ENGINE_INSTANCE.
>> >> +	 */
>> >> +	DRM_XE_OA_PROP_OA_ENGINE_CLASS,
>> >> +
>> >> +	/**
>> >> +	 * This parameter specifies the engine instance and must be passed along
>> >> +	 * with DRM_XE_OA_PROP_OA_ENGINE_CLASS.
>> >> +	 */
>> >> +	DRM_XE_OA_PROP_OA_ENGINE_INSTANCE,
>> >
>> > Because oa_unit_id has been introduced above in
>> > drm_xe_engine_class_instance, should we remove these engine class/instance
>> > properties? Since it seems OA streams can be opened directly against the oa
>> > unit identified by oa_unit_id. And the driver can itself figure out the
>> > engine class/instance from the oa_unit_id?
>>
>> Agree for the OA buffer use case.
>>
>> For query, we have used the class:instance to enable query support for
>> specific engine instance. If we can work around that somehow, then we can
>> do away with these 2 params. More like enable query for all engines that
>> belong to the OAG unit. For render, it is straight forward since we have
>> one render per OAG unit. For compute, multiple compute instances can map to
>> one OAG unit and only one instance can support the query. So user may want
>> to choose which instance that is. Although, I would just simplify it and
>> support only instance 0 of compute. If UMD is okay with it, then we should
>> be good.
>
>Can we enable the query (I guess "query" is MI_RPC) on all attached compute
>engines and have the UMD execute the query on any of the attached engines?
>Or is this mode of operation never been tried out before so risky?

We cannot, since that is gated by a global configuration in HW that 
selects a specific instance to enable the query for compute (ccs_select 
to be specific). I think the limitation is that HW has only one OAC unit 
and only one ccs can use it.

Umesh

>
>Ashutosh
>
>>
>> Media engines do not support query, so we should be good for OAM.
>>
>> >
>> > Separately, there is also the question of whether we want to share the Xe
>> > OA IGT code with i915 as was done for this series. Since duplicating the
>> > IGT code as well as all the perf tools seems a bit much.
>> >
>> > Thanks.
>> > --
>> > Ashutosh