Re: [Intel-gfx] [RFC PATCH 60/97] drm/i915: Track 'serial' counts for virtual engines

[Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>]

On 06/05/2021 20:14, Matthew Brost wrote:
> From: John Harrison <John.C.Harrison@xxxxxxxxx>
>
> The serial number tracking of engines happens at the backend of
> request submission and was expecting to only be given physical
> engines. However, in GuC submission mode, the decomposition of virtual
> to physical engines does not happen in i915. Instead, requests are
> submitted to their virtual engine mask all the way through to the
> hardware (i.e. to GuC). This would mean that the heart beat code
> thinks the physical engines are idle due to the serial number not
> incrementing.
>
> This patch updates the tracking to decompose virtual engines into
> their physical constituents and tracks the request against each. This
> is not entirely accurate as the GuC will only be issuing the request
> to one physical engine. However, it is the best that i915 can do given
> that it has no knowledge of the GuC's scheduling decisions.

Commit text sounds a bit defeatist. I think instead of making up the 
serial counts, which has downsides (could you please document in the 
commit what they are), we should think how to design things properly.

Regards,

Tvrtko

> Signed-off-by: John Harrison <John.C.Harrison@xxxxxxxxx>
> Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
> ---
>   drivers/gpu/drm/i915/gt/intel_engine_types.h     |  2 ++
>   .../gpu/drm/i915/gt/intel_execlists_submission.c |  6 ++++++
>   drivers/gpu/drm/i915/gt/intel_ring_submission.c  |  6 ++++++
>   drivers/gpu/drm/i915/gt/mock_engine.c            |  6 ++++++
>   .../gpu/drm/i915/gt/uc/intel_guc_submission.c    | 16 ++++++++++++++++
>   drivers/gpu/drm/i915/i915_request.c              |  4 +++-
>   6 files changed, 39 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> index 86302e6d86b2..e2b5cda6dbc4 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> @@ -389,6 +389,8 @@ struct intel_engine_cs {
>   	void		(*park)(struct intel_engine_cs *engine);
>   	void		(*unpark)(struct intel_engine_cs *engine);
>   
> +	void		(*bump_serial)(struct intel_engine_cs *engine);
> +
>   	void		(*set_default_submission)(struct intel_engine_cs *engine);
>   
>   	const struct intel_context_ops *cops;
> diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> index ae12d7f19ecd..02880ea5d693 100644
> --- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> +++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> @@ -3199,6 +3199,11 @@ static void execlists_release(struct intel_engine_cs *engine)
>   	lrc_fini_wa_ctx(engine);
>   }
>   
> +static void execlist_bump_serial(struct intel_engine_cs *engine)
> +{
> +	engine->serial++;
> +}
> +
>   static void
>   logical_ring_default_vfuncs(struct intel_engine_cs *engine)
>   {
> @@ -3208,6 +3213,7 @@ logical_ring_default_vfuncs(struct intel_engine_cs *engine)
>   
>   	engine->cops = &execlists_context_ops;
>   	engine->request_alloc = execlists_request_alloc;
> +	engine->bump_serial = execlist_bump_serial;
>   
>   	engine->reset.prepare = execlists_reset_prepare;
>   	engine->reset.rewind = execlists_reset_rewind;
> diff --git a/drivers/gpu/drm/i915/gt/intel_ring_submission.c b/drivers/gpu/drm/i915/gt/intel_ring_submission.c
> index 14aa31879a37..39dd7c4ed0a9 100644
> --- a/drivers/gpu/drm/i915/gt/intel_ring_submission.c
> +++ b/drivers/gpu/drm/i915/gt/intel_ring_submission.c
> @@ -1045,6 +1045,11 @@ static void setup_irq(struct intel_engine_cs *engine)
>   	}
>   }
>   
> +static void ring_bump_serial(struct intel_engine_cs *engine)
> +{
> +	engine->serial++;
> +}
> +
>   static void setup_common(struct intel_engine_cs *engine)
>   {
>   	struct drm_i915_private *i915 = engine->i915;
> @@ -1064,6 +1069,7 @@ static void setup_common(struct intel_engine_cs *engine)
>   
>   	engine->cops = &ring_context_ops;
>   	engine->request_alloc = ring_request_alloc;
> +	engine->bump_serial = ring_bump_serial;
>   
>   	/*
>   	 * Using a global execution timeline; the previous final breadcrumb is
> diff --git a/drivers/gpu/drm/i915/gt/mock_engine.c b/drivers/gpu/drm/i915/gt/mock_engine.c
> index bd005c1b6fd5..97b10fd60b55 100644
> --- a/drivers/gpu/drm/i915/gt/mock_engine.c
> +++ b/drivers/gpu/drm/i915/gt/mock_engine.c
> @@ -292,6 +292,11 @@ static void mock_engine_release(struct intel_engine_cs *engine)
>   	intel_engine_fini_retire(engine);
>   }
>   
> +static void mock_bump_serial(struct intel_engine_cs *engine)
> +{
> +	engine->serial++;
> +}
> +
>   struct intel_engine_cs *mock_engine(struct drm_i915_private *i915,
>   				    const char *name,
>   				    int id)
> @@ -318,6 +323,7 @@ struct intel_engine_cs *mock_engine(struct drm_i915_private *i915,
>   
>   	engine->base.cops = &mock_context_ops;
>   	engine->base.request_alloc = mock_request_alloc;
> +	engine->base.bump_serial = mock_bump_serial;
>   	engine->base.emit_flush = mock_emit_flush;
>   	engine->base.emit_fini_breadcrumb = mock_emit_breadcrumb;
>   	engine->base.submit_request = mock_submit_request;
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> index dc79d287c50a..f0e5731bcef6 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -1500,6 +1500,20 @@ static void guc_release(struct intel_engine_cs *engine)
>   	lrc_fini_wa_ctx(engine);
>   }
>   
> +static void guc_bump_serial(struct intel_engine_cs *engine)
> +{
> +	engine->serial++;
> +}
> +
> +static void virtual_guc_bump_serial(struct intel_engine_cs *engine)
> +{
> +	struct intel_engine_cs *e;
> +	intel_engine_mask_t tmp, mask = engine->mask;
> +
> +	for_each_engine_masked(e, engine->gt, mask, tmp)
> +		e->serial++;
> +}
> +
>   static void guc_default_vfuncs(struct intel_engine_cs *engine)
>   {
>   	/* Default vfuncs which can be overridden by each engine. */
> @@ -1508,6 +1522,7 @@ static void guc_default_vfuncs(struct intel_engine_cs *engine)
>   
>   	engine->cops = &guc_context_ops;
>   	engine->request_alloc = guc_request_alloc;
> +	engine->bump_serial = guc_bump_serial;
>   
>   	engine->sched_engine->schedule = i915_schedule;
>   
> @@ -1843,6 +1858,7 @@ guc_create_virtual(struct intel_engine_cs **siblings, unsigned int count)
>   
>   	ve->base.cops = &virtual_guc_context_ops;
>   	ve->base.request_alloc = guc_request_alloc;
> +	ve->base.bump_serial = virtual_guc_bump_serial;
>   
>   	ve->base.submit_request = guc_submit_request;
>   
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index 9542a5baa45a..127d60b36422 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -692,7 +692,9 @@ bool __i915_request_submit(struct i915_request *request)
>   				     request->ring->vaddr + request->postfix);
>   
>   	trace_i915_request_execute(request);
> -	engine->serial++;
> +	if (engine->bump_serial)
> +		engine->bump_serial(engine);
> +
>   	result = true;
>   
>   	GEM_BUG_ON(test_bit(I915_FENCE_FLAG_ACTIVE, &request->fence.flags));