Re: [PATCH 03/15] drm/i915: Drop spinlocks around adding to the client request list

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

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

> Adding to the tail of the client request list as the only other user is
> in the throttle ioctl that iterates forwards over the list. It only
> needs protection against deletion of a request as it reads it, it simply
> won't see a new request added to the end of the list, or it would be too
> early and rejected. We can further reduce the number of spinlocks
> required when throttling by removing stale requests from the client_list
> as we throttle.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>


> ---
>  drivers/gpu/drm/i915/i915_debugfs.c        |  2 +-
>  drivers/gpu/drm/i915/i915_gem.c            | 14 ++++++------
>  drivers/gpu/drm/i915/i915_gem_execbuffer.c | 13 ++++++++----
>  drivers/gpu/drm/i915/i915_gem_request.c    | 34 ++++++------------------------
>  drivers/gpu/drm/i915/i915_gem_request.h    |  4 +---
>  5 files changed, 23 insertions(+), 44 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 1a28b5279bec..ddae8e442176 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -506,7 +506,7 @@ static int i915_gem_object_info(struct seq_file *m, void *data)
>  		mutex_lock(&dev->struct_mutex);
>  		request = list_first_entry_or_null(&file_priv->mm.request_list,
>  						   struct drm_i915_gem_request,
> -						   client_list);
> +						   client_link);
>  		rcu_read_lock();
>  		task = pid_task(request && request->ctx->pid ?
>  				request->ctx->pid : file->pid,
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index de1fc98e041d..92ab989bb05f 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -3667,16 +3667,14 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
>  		return -EIO;
>  
>  	spin_lock(&file_priv->mm.lock);
> -	list_for_each_entry(request, &file_priv->mm.request_list, client_list) {
> +	list_for_each_entry(request, &file_priv->mm.request_list, client_link) {
>  		if (time_after_eq(request->emitted_jiffies, recent_enough))
>  			break;
>  
> -		/*
> -		 * Note that the request might not have been submitted yet.
> -		 * In which case emitted_jiffies will be zero.
> -		 */
> -		if (!request->emitted_jiffies)
> -			continue;
> +		if (target) {
> +			list_del(&target->client_link);
> +			target->file_priv = NULL;
> +		}
>  
>  		target = request;
>  	}
> @@ -4735,7 +4733,7 @@ void i915_gem_release(struct drm_device *dev, struct drm_file *file)
>  	 * file_priv.
>  	 */
>  	spin_lock(&file_priv->mm.lock);
> -	list_for_each_entry(request, &file_priv->mm.request_list, client_list)
> +	list_for_each_entry(request, &file_priv->mm.request_list, client_link)
>  		request->file_priv = NULL;
>  	spin_unlock(&file_priv->mm.lock);
>  
> diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> index e8ffe0c9a20e..2b570d0b2392 100644
> --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> @@ -1420,6 +1420,14 @@ i915_gem_execbuffer_parse(struct intel_engine_cs *engine,
>  	return vma;
>  }
>  
> +static void
> +add_to_client(struct drm_i915_gem_request *req,
> +	      struct drm_file *file)
> +{
> +	req->file_priv = file->driver_priv;
> +	list_add_tail(&req->client_link, &req->file_priv->mm.request_list);
> +}
> +
>  static int
>  execbuf_submit(struct i915_execbuffer_params *params,
>  	       struct drm_i915_gem_execbuffer2 *args,
> @@ -1507,6 +1515,7 @@ execbuf_submit(struct i915_execbuffer_params *params,
>  		return ret;
>  
>  	i915_gem_execbuffer_move_to_active(vmas, params->request);
> +	add_to_client(params->request, params->file);
>  
>  	return 0;
>  }
> @@ -1886,10 +1895,6 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
>  	 */
>  	params->request->batch = params->batch;
>  
> -	ret = i915_gem_request_add_to_client(params->request, file);
> -	if (ret)
> -		goto err_request;
> -
>  	/*
>  	 * Save assorted stuff away to pass through to *_submission().
>  	 * NB: This data should be 'persistent' and not local as it will
> diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
> index 3a159cac2172..5bca3e25bf61 100644
> --- a/drivers/gpu/drm/i915/i915_gem_request.c
> +++ b/drivers/gpu/drm/i915/i915_gem_request.c
> @@ -82,42 +82,20 @@ const struct dma_fence_ops i915_fence_ops = {
>  	.release = i915_fence_release,
>  };
>  
> -int i915_gem_request_add_to_client(struct drm_i915_gem_request *req,
> -				   struct drm_file *file)
> -{
> -	struct drm_i915_private *dev_private;
> -	struct drm_i915_file_private *file_priv;
> -
> -	WARN_ON(!req || !file || req->file_priv);
> -
> -	if (!req || !file)
> -		return -EINVAL;
> -
> -	if (req->file_priv)
> -		return -EINVAL;
> -
> -	dev_private = req->i915;
> -	file_priv = file->driver_priv;
> -
> -	spin_lock(&file_priv->mm.lock);
> -	req->file_priv = file_priv;
> -	list_add_tail(&req->client_list, &file_priv->mm.request_list);
> -	spin_unlock(&file_priv->mm.lock);
> -
> -	return 0;
> -}
> -
>  static inline void
>  i915_gem_request_remove_from_client(struct drm_i915_gem_request *request)
>  {
> -	struct drm_i915_file_private *file_priv = request->file_priv;
> +	struct drm_i915_file_private *file_priv;
>  
> +	file_priv = request->file_priv;
>  	if (!file_priv)
>  		return;
>  
>  	spin_lock(&file_priv->mm.lock);
> -	list_del(&request->client_list);
> -	request->file_priv = NULL;
> +	if (request->file_priv) {
> +		list_del(&request->client_link);
> +		request->file_priv = NULL;
> +	}
>  	spin_unlock(&file_priv->mm.lock);
>  }
>  
> diff --git a/drivers/gpu/drm/i915/i915_gem_request.h b/drivers/gpu/drm/i915/i915_gem_request.h
> index cc24a6c72748..1edc0fa7794c 100644
> --- a/drivers/gpu/drm/i915/i915_gem_request.h
> +++ b/drivers/gpu/drm/i915/i915_gem_request.h
> @@ -191,7 +191,7 @@ struct drm_i915_gem_request {
>  
>  	struct drm_i915_file_private *file_priv;
>  	/** file_priv list entry for this request */
> -	struct list_head client_list;
> +	struct list_head client_link;
>  };
>  
>  extern const struct dma_fence_ops i915_fence_ops;
> @@ -204,8 +204,6 @@ static inline bool dma_fence_is_i915(const struct dma_fence *fence)
>  struct drm_i915_gem_request * __must_check
>  i915_gem_request_alloc(struct intel_engine_cs *engine,
>  		       struct i915_gem_context *ctx);
> -int i915_gem_request_add_to_client(struct drm_i915_gem_request *req,
> -				   struct drm_file *file);
>  void i915_gem_request_retire_upto(struct drm_i915_gem_request *req);
>  
>  static inline struct drm_i915_gem_request *
> -- 
> 2.11.0
>
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