Re: [Intel-gfx] [PATCH 30/57] drm/i915: Move timeslicing flag to scheduler

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

On 01/02/2021 08:56, Chris Wilson wrote:
> Whether a scheduler chooses to implement timeslicing is up to it, and
> not an underlying property of the HW engine. The scheduler does depend
> on the HW supporting preemption.

Therefore, continuing on the comment I made in the previous patch, if we 
had a helper with which engine would request scheduling (setting the 
tasklet), if it passed in a pointer to itself, scheduler would then be 
able to inspect if the engine supports preemption and so set its own 
internal flag. Makes sense? It would require something like:

   i915_sched_enable_scheduling(se, engine, tasklet)

Or something like that if my memory still holds.

Regards,

Tvrtko

> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/gt/intel_engine.h         |  6 ++++++
>   drivers/gpu/drm/i915/gt/intel_engine_types.h   | 18 ++++--------------
>   .../drm/i915/gt/intel_execlists_submission.c   |  9 ++++++---
>   drivers/gpu/drm/i915/gt/selftest_execlists.c   |  2 +-
>   drivers/gpu/drm/i915/i915_scheduler_types.h    | 10 ++++++++++
>   5 files changed, 27 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine.h b/drivers/gpu/drm/i915/gt/intel_engine.h
> index 4f0163457aed..ca3a9cb06328 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine.h
> +++ b/drivers/gpu/drm/i915/gt/intel_engine.h
> @@ -279,4 +279,10 @@ intel_engine_flush_scheduler(struct intel_engine_cs *engine)
>   	i915_sched_flush(intel_engine_get_scheduler(engine));
>   }
>   
> +static inline bool
> +intel_engine_has_timeslices(struct intel_engine_cs *engine)
> +{
> +	return i915_sched_has_timeslices(intel_engine_get_scheduler(engine));
> +}
> +
>   #endif /* _INTEL_RINGBUFFER_H_ */
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> index a3024a0de1de..96a0aec29672 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> @@ -442,11 +442,10 @@ struct intel_engine_cs {
>   #define I915_ENGINE_SUPPORTS_STATS   BIT(1)
>   #define I915_ENGINE_HAS_PREEMPTION   BIT(2)
>   #define I915_ENGINE_HAS_SEMAPHORES   BIT(3)
> -#define I915_ENGINE_HAS_TIMESLICES   BIT(4)
> -#define I915_ENGINE_NEEDS_BREADCRUMB_TASKLET BIT(5)
> -#define I915_ENGINE_IS_VIRTUAL       BIT(6)
> -#define I915_ENGINE_HAS_RELATIVE_MMIO BIT(7)
> -#define I915_ENGINE_REQUIRES_CMD_PARSER BIT(8)
> +#define I915_ENGINE_NEEDS_BREADCRUMB_TASKLET BIT(4)
> +#define I915_ENGINE_IS_VIRTUAL       BIT(5)
> +#define I915_ENGINE_HAS_RELATIVE_MMIO BIT(6)
> +#define I915_ENGINE_REQUIRES_CMD_PARSER BIT(7)
>   	unsigned int flags;
>   
>   	/*
> @@ -541,15 +540,6 @@ intel_engine_has_semaphores(const struct intel_engine_cs *engine)
>   	return engine->flags & I915_ENGINE_HAS_SEMAPHORES;
>   }
>   
> -static inline bool
> -intel_engine_has_timeslices(const struct intel_engine_cs *engine)
> -{
> -	if (!IS_ACTIVE(CONFIG_DRM_I915_TIMESLICE_DURATION))
> -		return false;
> -
> -	return engine->flags & I915_ENGINE_HAS_TIMESLICES;
> -}
> -
>   static inline bool
>   intel_engine_needs_breadcrumb_tasklet(const struct intel_engine_cs *engine)
>   {
> diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> index 3217cb4369ad..d4b6d262265a 100644
> --- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> +++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> @@ -1023,7 +1023,7 @@ static bool needs_timeslice(const struct intel_engine_cs *engine,
>   {
>   	const struct i915_sched *se = &engine->sched;
>   
> -	if (!intel_engine_has_timeslices(engine))
> +	if (!i915_sched_has_timeslices(se))
>   		return false;
>   
>   	/* If not currently active, or about to switch, wait for next event */
> @@ -2918,8 +2918,6 @@ logical_ring_default_vfuncs(struct intel_engine_cs *engine)
>   		engine->flags |= I915_ENGINE_HAS_SEMAPHORES;
>   		if (can_preempt(engine)) {
>   			engine->flags |= I915_ENGINE_HAS_PREEMPTION;
> -			if (IS_ACTIVE(CONFIG_DRM_I915_TIMESLICE_DURATION))
> -				engine->flags |= I915_ENGINE_HAS_TIMESLICES;
>   		}
>   	}
>   
> @@ -2927,6 +2925,11 @@ logical_ring_default_vfuncs(struct intel_engine_cs *engine)
>   		engine->emit_bb_start = gen8_emit_bb_start;
>   	else
>   		engine->emit_bb_start = gen8_emit_bb_start_noarb;
> +
> +	if (IS_ACTIVE(CONFIG_DRM_I915_TIMESLICE_DURATION) &&
> +	    intel_engine_has_preemption(engine))
> +		__set_bit(I915_SCHED_HAS_TIMESLICES_BIT,
> +			  &engine->sched.flags);
>   }
>   
>   static void logical_ring_default_irqs(struct intel_engine_cs *engine)
> diff --git a/drivers/gpu/drm/i915/gt/selftest_execlists.c b/drivers/gpu/drm/i915/gt/selftest_execlists.c
> index cfc0f4b9fbc5..147cbfd6dec0 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_execlists.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_execlists.c
> @@ -3825,7 +3825,7 @@ static unsigned int
>   __select_siblings(struct intel_gt *gt,
>   		  unsigned int class,
>   		  struct intel_engine_cs **siblings,
> -		  bool (*filter)(const struct intel_engine_cs *))
> +		  bool (*filter)(struct intel_engine_cs *))
>   {
>   	unsigned int n = 0;
>   	unsigned int inst;
> diff --git a/drivers/gpu/drm/i915/i915_scheduler_types.h b/drivers/gpu/drm/i915/i915_scheduler_types.h
> index cb1eddb7edc8..dfb29b8c2bee 100644
> --- a/drivers/gpu/drm/i915/i915_scheduler_types.h
> +++ b/drivers/gpu/drm/i915/i915_scheduler_types.h
> @@ -12,12 +12,14 @@
>   #include <linux/workqueue.h>
>   
>   #include "i915_priolist_types.h"
> +#include "i915_utils.h"
>   
>   struct drm_printer;
>   struct i915_request;
>   
>   enum {
>   	I915_SCHED_ACTIVE_BIT = 0,
> +	I915_SCHED_HAS_TIMESLICES_BIT,
>   };
>   
>   /**
> @@ -184,4 +186,12 @@ static inline bool i915_sched_is_active(const struct i915_sched *se)
>   	return test_bit(I915_SCHED_ACTIVE_BIT, &se->flags);
>   }
>   
> +static inline bool i915_sched_has_timeslices(const struct i915_sched *se)
> +{
> +	if (!IS_ACTIVE(CONFIG_DRM_I915_TIMESLICE_DURATION))
> +		return false;
> +
> +	return test_bit(I915_SCHED_HAS_TIMESLICES_BIT, &se->flags);
> +}
> +
>   #endif /* _I915_SCHEDULER_TYPES_H_ */
> 
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