Re: [PATCH v2 5/5] drm/msm: subclass work object for vblank events

[Sean Paul <sean-p7yTbzM4H96eqtR555YLDQ@public.gmane.org>]

On Tue, Nov 06, 2018 at 02:36:30PM -0800, Jeykumar Sankaran wrote:
> msm maintains a separate structure to define vblank
> work definitions and a list to track events submitted
> to the workqueue. We can avoid this redundant list
> and its protection mechanism, if we subclass the
> work object to encapsulate vblank event parameters.
> 
> changes in v2:
> 	- subclass optimization on system wq (Sean Paul)

I wouldn't do it like this, tbh. One problem is that you've lost your flush() on
unbind, so there's no way to know if you have workers in the wild waiting to
enable/disable vblank.

Another issues is that AFAICT, we don't need a queue of enables/disables, but
rather just the last requested state (ie: should we be on or off). So things
don't need to be this complicated (and we're possibly thrashing vblank on/off
for no reason).

I'm still of the mind that you should just make this synchronous and be done
with the threads (especially since we're still uncovering/introducing races!).

Sean

> 
> Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>
> ---
>  drivers/gpu/drm/msm/msm_drv.c | 67 +++++++++++++------------------------------
>  drivers/gpu/drm/msm/msm_drv.h |  7 -----
>  2 files changed, 20 insertions(+), 54 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> index 6d6c73b..8da5be2 100644
> --- a/drivers/gpu/drm/msm/msm_drv.c
> +++ b/drivers/gpu/drm/msm/msm_drv.c
> @@ -203,61 +203,44 @@ u32 msm_readl(const void __iomem *addr)
>  	return val;
>  }
>  
> -struct vblank_event {
> -	struct list_head node;
> +struct msm_vblank_work {
> +	struct work_struct work;
>  	int crtc_id;
>  	bool enable;
> +	struct msm_drm_private *priv;
>  };
>  
>  static void vblank_ctrl_worker(struct work_struct *work)
>  {
> -	struct msm_vblank_ctrl *vbl_ctrl = container_of(work,
> -						struct msm_vblank_ctrl, work);
> -	struct msm_drm_private *priv = container_of(vbl_ctrl,
> -					struct msm_drm_private, vblank_ctrl);
> +	struct msm_vblank_work *vbl_work = container_of(work,
> +						struct msm_vblank_work, work);
> +	struct msm_drm_private *priv = vbl_work->priv;
>  	struct msm_kms *kms = priv->kms;
> -	struct vblank_event *vbl_ev, *tmp;
> -	unsigned long flags;
> -
> -	spin_lock_irqsave(&vbl_ctrl->lock, flags);
> -	list_for_each_entry_safe(vbl_ev, tmp, &vbl_ctrl->event_list, node) {
> -		list_del(&vbl_ev->node);
> -		spin_unlock_irqrestore(&vbl_ctrl->lock, flags);
> -
> -		if (vbl_ev->enable)
> -			kms->funcs->enable_vblank(kms,
> -						priv->crtcs[vbl_ev->crtc_id]);
> -		else
> -			kms->funcs->disable_vblank(kms,
> -						priv->crtcs[vbl_ev->crtc_id]);
>  
> -		kfree(vbl_ev);
> -
> -		spin_lock_irqsave(&vbl_ctrl->lock, flags);
> -	}
> +	if (vbl_work->enable)
> +		kms->funcs->enable_vblank(kms, priv->crtcs[vbl_work->crtc_id]);
> +	else
> +		kms->funcs->disable_vblank(kms,	priv->crtcs[vbl_work->crtc_id]);
>  
> -	spin_unlock_irqrestore(&vbl_ctrl->lock, flags);
> +	kfree(vbl_work);
>  }
>  
>  static int vblank_ctrl_queue_work(struct msm_drm_private *priv,
>  					int crtc_id, bool enable)
>  {
> -	struct msm_vblank_ctrl *vbl_ctrl = &priv->vblank_ctrl;
> -	struct vblank_event *vbl_ev;
> -	unsigned long flags;
> +	struct msm_vblank_work *vbl_work;
>  
> -	vbl_ev = kzalloc(sizeof(*vbl_ev), GFP_ATOMIC);
> -	if (!vbl_ev)
> +	vbl_work = kzalloc(sizeof(*vbl_work), GFP_ATOMIC);
> +	if (!vbl_work)
>  		return -ENOMEM;
>  
> -	vbl_ev->crtc_id = crtc_id;
> -	vbl_ev->enable = enable;
> +	INIT_WORK(&vbl_work->work, vblank_ctrl_worker);
>  
> -	spin_lock_irqsave(&vbl_ctrl->lock, flags);
> -	list_add_tail(&vbl_ev->node, &vbl_ctrl->event_list);
> -	spin_unlock_irqrestore(&vbl_ctrl->lock, flags);
> +	vbl_work->crtc_id = crtc_id;
> +	vbl_work->enable = enable;
> +	vbl_work->priv = priv;
>  
> -	schedule_work(&vbl_ctrl->work);
> +	schedule_work(&vbl_work->work);
>  
>  	return 0;
>  }
> @@ -269,14 +252,13 @@ static int msm_drm_uninit(struct device *dev)
>  	struct msm_drm_private *priv = ddev->dev_private;
>  	struct msm_kms *kms = priv->kms;
>  	struct msm_mdss *mdss = priv->mdss;
> -	struct msm_vblank_ctrl *vbl_ctrl = &priv->vblank_ctrl;
> -	struct vblank_event *vbl_ev, *tmp;
>  	int i;
>  
>  	/* We must cancel and cleanup any pending vblank enable/disable
>  	 * work before drm_irq_uninstall() to avoid work re-enabling an
>  	 * irq after uninstall has disabled it.
>  	 */
> +
>  	msm_gem_shrinker_cleanup(ddev);
>  
>  	drm_kms_helper_poll_fini(ddev);
> @@ -292,12 +274,6 @@ static int msm_drm_uninit(struct device *dev)
>  #endif
>  	drm_mode_config_cleanup(ddev);
>  
> -	flush_work(&vbl_ctrl->work);
> -	list_for_each_entry_safe(vbl_ev, tmp, &vbl_ctrl->event_list, node) {
> -		list_del(&vbl_ev->node);
> -		kfree(vbl_ev);
> -	}
> -
>  	/* clean up event worker threads */
>  	for (i = 0; i < priv->num_crtcs; i++) {
>  		if (priv->event_thread[i].thread) {
> @@ -469,9 +445,6 @@ static int msm_drm_init(struct device *dev, struct drm_driver *drv)
>  	priv->wq = alloc_ordered_workqueue("msm", 0);
>  
>  	INIT_LIST_HEAD(&priv->inactive_list);
> -	INIT_LIST_HEAD(&priv->vblank_ctrl.event_list);
> -	INIT_WORK(&priv->vblank_ctrl.work, vblank_ctrl_worker);
> -	spin_lock_init(&priv->vblank_ctrl.lock);
>  
>  	drm_mode_config_init(ddev);
>  
> diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
> index 05d33a7..d4cbde2 100644
> --- a/drivers/gpu/drm/msm/msm_drv.h
> +++ b/drivers/gpu/drm/msm/msm_drv.h
> @@ -77,12 +77,6 @@ enum msm_mdp_plane_property {
>  	PLANE_PROP_MAX_NUM
>  };
>  
> -struct msm_vblank_ctrl {
> -	struct work_struct work;
> -	struct list_head event_list;
> -	spinlock_t lock;
> -};
> -
>  #define MSM_GPU_MAX_RINGS 4
>  #define MAX_H_TILES_PER_DISPLAY 2
>  
> @@ -225,7 +219,6 @@ struct msm_drm_private {
>  	struct notifier_block vmap_notifier;
>  	struct shrinker shrinker;
>  
> -	struct msm_vblank_ctrl vblank_ctrl;
>  	struct drm_atomic_state *pm_state;
>  };
>  
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
> 
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-- 
Sean Paul, Software Engineer, Google / Chromium OS
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