Re: [PATCH] drm/i915/guc: Defer LRC context unpin or release

[Yu Dai <yu.dai@intel.com>]

Sorry for wrong patch. Please forget about his one. Another one will be 
submitted.

Alex

On 11/06/2015 01:56 PM, yu.dai@intel.com wrote:
> From: Alex Dai <yu.dai@intel.com>
>
> Can't immediately free LRC context (neither unpin it) even all
> its referenced requests are completed, because HW still need a
> short period of time to save data to LRC status page. It is safe
> to free LRC when HW completes a request from a different LRC.
>
> Move LRC to ring->last_unpin_ctx when its pin count reaches zero.
> Increase ctx refcount to make sure it won't be freed immediately.
> When HW complete the next request from a different LRC, release
> the last yet-to-be-released one. In the case it is pinned again,
> simply decrease its refcount.
>
> Signed-off-by: Alex Dai <yu.dai@intel.com>
> ---
>   drivers/gpu/drm/i915/intel_lrc.c        | 54 ++++++++++++++++++++++++++++-----
>   drivers/gpu/drm/i915/intel_ringbuffer.h |  1 +
>   2 files changed, 47 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 06180dc..da01d72 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -1051,6 +1051,14 @@ static int intel_lr_context_pin(struct drm_i915_gem_request *rq)
>   		if (ret)
>   			goto reset_pin_count;
>   	}
> +
> +	/* If we are holding this LRC from last unpin, unref it here. */
> +	if (ring->last_unpin_ctx == rq->ctx) {
> +		rq->ctx->engine[ring->id].pin_count--;
> +		i915_gem_context_unreference(rq->ctx);
> +		ring->last_unpin_ctx = NULL;
> +	}
> +
>   	return ret;
>   
>   reset_pin_count:
> @@ -1058,18 +1066,46 @@ reset_pin_count:
>   	return ret;
>   }
>   
> +static void
> +lrc_unpin_last_ctx(struct intel_engine_cs *ring)
> +{
> +	struct intel_context *ctx = ring->last_unpin_ctx;
> +	struct drm_i915_gem_object *ctx_obj;
> +
> +	if (!ctx)
> +		return;
> +
> +	i915_gem_object_ggtt_unpin(ctx->engine[ring->id].state);
> +	intel_unpin_ringbuffer_obj(ctx->engine[ring->id].ringbuf);
> +
> +	WARN_ON(--ctx->engine[ring->id].pin_count);
> +	i915_gem_context_unreference(ctx);
> +
> +	ring->last_unpin_ctx = NULL;
> +}
> +
>   void intel_lr_context_unpin(struct drm_i915_gem_request *rq)
>   {
>   	struct intel_engine_cs *ring = rq->ring;
> -	struct drm_i915_gem_object *ctx_obj = rq->ctx->engine[ring->id].state;
> -	struct intel_ringbuffer *ringbuf = rq->ringbuf;
>   
> -	if (ctx_obj) {
> -		WARN_ON(!mutex_is_locked(&ring->dev->struct_mutex));
> -		if (--rq->ctx->engine[ring->id].pin_count == 0) {
> -			intel_unpin_ringbuffer_obj(ringbuf);
> -			i915_gem_object_ggtt_unpin(ctx_obj);
> -		}
> +	if (!rq->ctx->engine[ring->id].state)
> +		return;
> +
> +	WARN_ON(!mutex_is_locked(&ring->dev->struct_mutex));
> +
> +	/* HW completes request from a different LRC, unpin the last one. */
> +	if (ring->last_unpin_ctx != rq->ctx)
> +		lrc_unpin_last_ctx(ring);
> +
> +	if (--rq->ctx->engine[ring->id].pin_count == 0) {
> +		/* Last one should be unpined already */
> +		WARN_ON(ring->last_unpin_ctx);
> +
> +		/* Keep the context pinned and ref-counted */
> +		rq->ctx->engine[ring->id].pin_count++;
> +		i915_gem_context_reference(rq->ctx);
> +
> +		ring->last_unpin_ctx = rq->ctx;
>   	}
>   }
>   
> @@ -1908,6 +1944,8 @@ void intel_logical_ring_cleanup(struct intel_engine_cs *ring)
>   	}
>   
>   	lrc_destroy_wa_ctx_obj(ring);
> +
> +	lrc_unpin_last_ctx(ring);
>   }
>   
>   static int logical_ring_init(struct drm_device *dev, struct intel_engine_cs *ring)
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
> index 58b1976..676d27f 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> @@ -267,6 +267,7 @@ struct  intel_engine_cs {
>   	spinlock_t execlist_lock;
>   	struct list_head execlist_queue;
>   	struct list_head execlist_retired_req_list;
> +	struct intel_context *last_unpin_ctx;
>   	u8 next_context_status_buffer;
>   	u32             irq_keep_mask; /* bitmask for interrupts that should not be masked */
>   	int		(*emit_request)(struct drm_i915_gem_request *request);

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