Re: [PATCH 1/4] drm/i915: Record the position of the start of the request

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

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

> Not only does it make for good documentation and debugging aide, but it is
> also vital for when we want to unwind requests - such as when throwing away
> an incomplete request.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Link: http://patchwork.freedesktop.org/patch/msgid/1470414607-32453-2-git-send-email-arun.siluvery@linux.intel.com
> ---
>  drivers/gpu/drm/i915/i915_drv.h         |  1 +
>  drivers/gpu/drm/i915/i915_gem_request.c | 13 +++++++++----
>  drivers/gpu/drm/i915/i915_gpu_error.c   |  6 ++++--
>  3 files changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index feec00f769e1..040c3b6300ac 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -557,6 +557,7 @@ struct drm_i915_error_state {
>  		struct drm_i915_error_request {
>  			long jiffies;
>  			u32 seqno;
> +			u32 head;
>  			u32 tail;
>  		} *requests;
>  
> diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
> index 6a1661643d3d..6c2553715263 100644
> --- a/drivers/gpu/drm/i915/i915_gem_request.c
> +++ b/drivers/gpu/drm/i915/i915_gem_request.c
> @@ -391,6 +391,13 @@ i915_gem_request_alloc(struct intel_engine_cs *engine,
>  	if (ret)
>  		goto err_ctx;
>  
> +	/* Record the position of the start of the request so that
> +	 * should we detect the updated seqno part-way through the
> +	 * GPU processing the request, we never over-estimate the
> +	 * position of the head.
> +	 */
> +	req->head = req->ring->tail;
> +
>  	return req;
>  
>  err_ctx:
> @@ -467,8 +474,6 @@ void __i915_add_request(struct drm_i915_gem_request *request,
>  
>  	trace_i915_gem_request_add(request);
>  
> -	request->head = request_start;

Nuke the local request_start also?

-Mika

> -
>  	/* Whilst this request exists, batch_obj will be on the
>  	 * active_list, and so will hold the active reference. Only when this
>  	 * request is retired will the the batch_obj be moved onto the
> @@ -489,10 +494,10 @@ void __i915_add_request(struct drm_i915_gem_request *request,
>  	list_add_tail(&request->link, &engine->request_list);
>  	list_add_tail(&request->ring_link, &ring->request_list);
>  
> -	/* Record the position of the start of the request so that
> +	/* Record the position of the start of the breadcrumb so that
>  	 * should we detect the updated seqno part-way through the
>  	 * GPU processing the request, we never over-estimate the
> -	 * position of the head.
> +	 * position of the ring's HEAD.
>  	 */
>  	request->postfix = ring->tail;
>  
> diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
> index eecb87063c88..c9e1246ecd36 100644
> --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> @@ -455,9 +455,10 @@ int i915_error_state_to_str(struct drm_i915_error_state_buf *m,
>  				   dev_priv->engine[i].name,
>  				   ee->num_requests);
>  			for (j = 0; j < ee->num_requests; j++) {
> -				err_printf(m, "  seqno 0x%08x, emitted %ld, tail 0x%08x\n",
> +				err_printf(m, "  seqno 0x%08x, emitted %ld, head 0x%08x tail 0x%08x\n",
>  					   ee->requests[j].seqno,
>  					   ee->requests[j].jiffies,
> +					   ee->requests[j].head,
>  					   ee->requests[j].tail);
>  			}
>  		}
> @@ -1205,7 +1206,8 @@ static void i915_gem_record_rings(struct drm_i915_private *dev_priv,
>  			erq = &ee->requests[count++];
>  			erq->seqno = request->fence.seqno;
>  			erq->jiffies = request->emitted_jiffies;
> -			erq->tail = request->postfix;
> +			erq->head = request->head;
> +			erq->tail = request->tail;
>  		}
>  	}
>  }
> -- 
> 2.8.1
>
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