Re: [PATCH 3/5] drm/i915: Mark up "sentinel" requests

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> Sometimes we want to emit a terminator request, a request that flushes
> the pipeline and allows no request to come after it. This can be used
> for a "preempt-to-idle" to ensure that upon processing the
> context-switch to that request, all other active contexts have been
> flushed.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/gt/intel_lrc.c |  6 ++++++
>  drivers/gpu/drm/i915/i915_request.h | 10 ++++++++--
>  2 files changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index 4e45cd972267..59a7e4eb7e2a 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -759,6 +759,9 @@ static bool can_merge_rq(const struct i915_request *prev,
>  	GEM_BUG_ON(prev == next);
>  	GEM_BUG_ON(!assert_priority_queue(prev, next));
>  
> +	if (i915_request_has_sentinel(prev))
> +		return false;
> +
>  	if (!can_merge_ctx(prev->hw_context, next->hw_context))
>  		return false;
>  
> @@ -1250,6 +1253,9 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>  				if (last->hw_context == rq->hw_context)
>  					goto done;
>  
> +				if (i915_request_has_sentinel(last))
> +					goto done;
> +
>  				/*
>  				 * If GVT overrides us we only ever submit
>  				 * port[0], leaving port[1] empty. Note that we
> diff --git a/drivers/gpu/drm/i915/i915_request.h b/drivers/gpu/drm/i915/i915_request.h
> index 313df3c37158..c41ecbe0bd0c 100644
> --- a/drivers/gpu/drm/i915/i915_request.h
> +++ b/drivers/gpu/drm/i915/i915_request.h
> @@ -217,8 +217,9 @@ struct i915_request {
>  	unsigned long emitted_jiffies;
>  
>  	unsigned long flags;
> -#define I915_REQUEST_WAITBOOST BIT(0)
> -#define I915_REQUEST_NOPREEMPT BIT(1)
> +#define I915_REQUEST_WAITBOOST	BIT(0)
> +#define I915_REQUEST_NOPREEMPT	BIT(1)
> +#define I915_REQUEST_SENTINEL	BIT(2)

Would it be possible to use 'empty' ie non payloadable
requests as a sentinel? (using the request->postfix).

Or is the advantage here that by attaching it as
a property, you avoid submitting an extra (empty)?

-Mika

>  
>  	/** timeline->request entry for this request */
>  	struct list_head link;
> @@ -443,6 +444,11 @@ static inline bool i915_request_has_nopreempt(const struct i915_request *rq)
>  	return unlikely(rq->flags & I915_REQUEST_NOPREEMPT);
>  }
>  
> +static inline bool i915_request_has_sentinel(const struct i915_request *rq)
> +{
> +	return unlikely(rq->flags & I915_REQUEST_SENTINEL);
> +}
> +
>  bool i915_retire_requests(struct drm_i915_private *i915);
>  
>  #endif /* I915_REQUEST_H */
> -- 
> 2.23.0.rc1
>
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