Re: [PATCH 2/3] drm/atomic: Use kthread worker for nonblocking commits

[Daniel Vetter <daniel@ffwll.ch>]

On Sat, Sep 19, 2020 at 12:37:25PM -0700, Rob Clark wrote:
> From: Rob Clark <robdclark@chromium.org>
> 
> This will allow us to more easily switch scheduling rules based on what
> userspace wants.
> 
> Signed-off-by: Rob Clark <robdclark@chromium.org>

I still think switching to the highpriority systemwq as a start (like i915
already does) would be a good first step no matter what we end up doing
for the android thing.
-Daniel

> ---
>  drivers/gpu/drm/drm_atomic_helper.c | 13 ++++++++----
>  include/drm/drm_atomic.h            | 31 +++++++++++++++++++++++++++++
>  2 files changed, 40 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 9e1ad493e689..75eeec5e7b10 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1659,11 +1659,11 @@ static void commit_tail(struct drm_atomic_state *old_state)
>  	drm_atomic_state_put(old_state);
>  }
>  
> -static void commit_work(struct work_struct *work)
> +static void commit_work(struct kthread_work *work)
>  {
>  	struct drm_atomic_state *state = container_of(work,
>  						      struct drm_atomic_state,
> -						      commit_work);
> +						      commit_kwork);
>  	commit_tail(state);
>  }
>  
> @@ -1797,6 +1797,7 @@ int drm_atomic_helper_commit(struct drm_device *dev,
>  			     struct drm_atomic_state *state,
>  			     bool nonblock)
>  {
> +	struct kthread_worker *worker = NULL;
>  	int ret;
>  
>  	if (state->async_update) {
> @@ -1814,7 +1815,7 @@ int drm_atomic_helper_commit(struct drm_device *dev,
>  	if (ret)
>  		return ret;
>  
> -	INIT_WORK(&state->commit_work, commit_work);
> +	kthread_init_work(&state->commit_kwork, commit_work);
>  
>  	ret = drm_atomic_helper_prepare_planes(dev, state);
>  	if (ret)
> @@ -1857,8 +1858,12 @@ int drm_atomic_helper_commit(struct drm_device *dev,
>  	 */
>  
>  	drm_atomic_state_get(state);
> +
>  	if (nonblock)
> -		queue_work(system_unbound_wq, &state->commit_work);
> +		worker = drm_atomic_pick_worker(state);
> +
> +	if (worker)
> +		kthread_queue_work(worker, &state->commit_kwork);
>  	else
>  		commit_tail(state);
>  
> diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> index d07c851d255b..8d0ee19953df 100644
> --- a/include/drm/drm_atomic.h
> +++ b/include/drm/drm_atomic.h
> @@ -373,8 +373,18 @@ struct drm_atomic_state {
>  	 *
>  	 * Work item which can be used by the driver or helpers to execute the
>  	 * commit without blocking.
> +	 *
> +	 * This is deprecated, use commit_kwork.
>  	 */
>  	struct work_struct commit_work;
> +
> +	/**
> +	 * @commit_kwork:
> +	 *
> +	 * Work item which can be used by the driver or helpers to execute the
> +	 * commit without blocking.
> +	 */
> +	struct kthread_work commit_kwork;
>  };
>  
>  void __drm_crtc_commit_free(struct kref *kref);
> @@ -954,6 +964,27 @@ void drm_state_dump(struct drm_device *dev, struct drm_printer *p);
>  		      (new_obj_state) = (__state)->private_objs[__i].new_state, 1); \
>  	     (__i)++)
>  
> +/**
> + * drm_atomic_pick_worker - helper to get kworker to use for nonblocking commit
> + * @state: the &drm_atomic_state for the commit
> + *
> + * Pick an appropriate worker for a given atomic update.  The first CRTC
> + * invovled in the atomic update is used to pick the worker, to prevent
> + * serializing multiple pageflips / atomic-updates on indenpendent CRTCs.
> + */
> +static inline struct kthread_worker *
> +drm_atomic_pick_worker(const struct drm_atomic_state *state)
> +{
> +	struct drm_crtc_state *crtc_state;
> +	struct drm_crtc *crtc;
> +	unsigned i;
> +
> +	for_each_new_crtc_in_state(state, crtc, crtc_state, i)
> +		return crtc->worker;
> +
> +	return NULL;
> +}
> +
>  /**
>   * drm_atomic_crtc_needs_modeset - compute combined modeset need
>   * @state: &drm_crtc_state for the CRTC
> -- 
> 2.26.2
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch