[Intel-gfx] [PATCH 01/19] drm/i915/perf: Fix OA filtering logic for GuC mode

[Dixit, Ashutosh]

On Fri, 09 Sep 2022 16:47:36 -0700, Dixit, Ashutosh wrote:
>
> On Tue, 23 Aug 2022 13:41:37 -0700, Umesh Nerlige Ramappa wrote:
> >
> > +/*
> > + * For execlist mode of submission, pick an unused context id
> > + * 0 - (NUM_CONTEXT_TAG -1) are used by other contexts
> > + * XXX_MAX_CONTEXT_HW_ID is used by idle context
> > + *
> > + * For GuC mode of submission read context id from the upper dword of the
> > + * EXECLIST_STATUS register.
> > + */
> > +static int gen12_get_render_context_id(struct i915_perf_stream *stream)
> > +{
> > +	u32 ctx_id, mask;
> > +	int ret;
> > +
> > +	if (intel_engine_uses_guc(stream->engine)) {
> > +		ret = gen12_guc_sw_ctx_id(stream->pinned_ctx, &ctx_id);
> > +		if (ret)
> > +			return ret;
> > +
> > +		mask = ((1U << GEN12_GUC_SW_CTX_ID_WIDTH) - 1) <<
> > +			(GEN12_GUC_SW_CTX_ID_SHIFT - 32);
> > +	} else if (GRAPHICS_VER_FULL(stream->engine->i915) >= IP_VER(12, 50)) {
> > +		ctx_id = (XEHP_MAX_CONTEXT_HW_ID - 1) <<
> > +			(XEHP_SW_CTX_ID_SHIFT - 32);
> > +
> > +		mask = ((1U << XEHP_SW_CTX_ID_WIDTH) - 1) <<
> > +			(XEHP_SW_CTX_ID_SHIFT - 32);
> > +	} else {
> > +		ctx_id = (GEN12_MAX_CONTEXT_HW_ID - 1) <<
> > +			 (GEN11_SW_CTX_ID_SHIFT - 32);
> > +
> > +		mask = ((1U << GEN11_SW_CTX_ID_WIDTH) - 1) <<
> > +			(GEN11_SW_CTX_ID_SHIFT - 32);
>
> Previously I missed that these ctx_id's for non-GuC cases are just
> constants. How does it work in these cases?

For the record, offline reply from Umesh for this question:

Looks like the SW context id is set to a unique value by the KMD for
execlist mode here - __execlists_schedule_in() as ccid. Later it is written
to the execlist port here (as lrc.desc) - execlists_submit_ports(). It's
just a unique value that the kmd determines. For OA we are setting a
ce->tag when OA use case is active and it used by the
__execlists_schedule_in().

Related commit from Chris - 2935ed5339c49

I think the reason why OA is setting it is because this value is not
assigned until __execlists_schedule_in() is called. For OA context, this
may happen much later. The code that Chris has added, just assigns a value
in OA and then uses it later in the __execlists_schedule_in() path.