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

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 06/05/2021 20:14, Matthew Brost wrote:
> From: John Harrison <John.C.Harrison@Intel.com>
> 
> 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.
> 
> Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> ---
>   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);
> +

As long as you have to handle null vfunc, you could make the patch way 
smaller by doing:

   if (engine->bump_serial)
	engine->bump_serial(engine);
   else
	engine->serial++;

Added bonus you avoid a function call with execlists making the patch 
not introduce a double penalty. Or just make bump_serial always point to 
a valid/default function. No need for both a new branch *and* a function 
call I think. I'd prefer the code snippet as above though.

Regards,

Tvrtko

>   	result = true;
>   
>   	GEM_BUG_ON(test_bit(I915_FENCE_FLAG_ACTIVE, &request->fence.flags));
>