[Intel-gfx] [PATCH v4 8/9] drm/i915/perf: Add engine class instance parameters to perf

[Umesh Nerlige Ramappa]

On Wed, Mar 08, 2023 at 10:08:13AM -0800, Dixit, Ashutosh wrote:
>On Tue, 07 Mar 2023 12:16:10 -0800, Umesh Nerlige Ramappa wrote:
>>
>
>Hi Umesh,
>
>> One or more engines map to a specific OA unit. All reports from these
>> engines are captured in the OA buffer managed by this OA unit.
>>
>> Current i915 OA implementation supports only the OAG unit. OAG primarily
>> caters to render engine, so i915 OA uses render as the default engine
>> in the OA implementation. Since there are more OA units on newer
>> hardware that map to other engines, allow user to pass engine class and
>> instance to select and program specific OA units.
>
>I believe there is another uapi issue to be resolved here: how the engines
>are associated with OA units, since from the point of view of the uapi
>there are multiple engines and multiple OA units (even if in the actual
>implementation at present there is only one OA unit per gt). In the
>internal tree we had added oa_unit_id to engine_info for this. So if
>multiple engines had the same oa_unit_id, user could pass class:instance of
>any of those engines to get oa data from that OA unit (and generally know
>how engines are hooked up to OA units (the OA unit topology)).
>
>So the question is even if we don't implement it as part of this series (or
>do we have to?) do we at least need to agree to that uapi which will be
>used to associate OA units with engines?

It did make more sense for xehpsdv and other platforms where we had 
multiple OA units per GT and each GT had render and/or compute engines.  
In those cases, media and compute/render UMDs may have needed to know 
that topology.

For MTL, I don't think that an end user will benefit from the 
engine<->oa_unit mapping because

(1) media and render are separate GTs
(2) there is just one OA unit per GT and
(3) assuming media and render/compute are separate UMDs,

That's also the reason why the corresponding IGT series just uses a 
static mapping for MTL.

If we come across a case where the UMD needs this info OR we are 
supporting a platform with multiple OA units per tile, we should add the 
topology.

Thanks,
Umesh

>
>Thanks.
>--
>Ashutosh