Re: [PATCH 1/2] drm/msm: use common display thread for dispatching vblank events

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

On Wed, Oct 31, 2018 at 05:19:04PM -0700, Jeykumar Sankaran wrote:
> DPU was using one thread per display to dispatch async
> commits and vblank requests. Since clean up already happened
> in msm to use the common thread for all the display commits,
> display threads are only used to cater vblank requests. Single
> thread is sufficient to do the job without any performance hits.
> 
> Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>
> ---
>  drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c |  6 +---
>  drivers/gpu/drm/msm/msm_drv.c               | 50 ++++++++++++-----------------
>  drivers/gpu/drm/msm/msm_drv.h               |  2 +-
>  3 files changed, 23 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> index 82c55ef..aff20f5 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> @@ -753,11 +753,7 @@ static int dpu_encoder_resource_control(struct drm_encoder *drm_enc,
>  	is_vid_mode = dpu_enc->disp_info.capabilities &
>  						MSM_DISPLAY_CAP_VID_MODE;
>  
> -	if (drm_enc->crtc->index >= ARRAY_SIZE(priv->disp_thread)) {
> -		DPU_ERROR("invalid crtc index\n");
> -		return -EINVAL;
> -	}
> -	disp_thread = &priv->disp_thread[drm_enc->crtc->index];
> +	disp_thread = &priv->disp_thread;
>  
>  	/*
>  	 * when idle_pc is not supported, process only KICKOFF, STOP and MODESET
> diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> index 9c9f7ff..1f384b3 100644
> --- a/drivers/gpu/drm/msm/msm_drv.c
> +++ b/drivers/gpu/drm/msm/msm_drv.c
> @@ -257,8 +257,7 @@ static int vblank_ctrl_queue_work(struct msm_drm_private *priv,
>  	list_add_tail(&vbl_ev->node, &vbl_ctrl->event_list);
>  	spin_unlock_irqrestore(&vbl_ctrl->lock, flags);
>  
> -	kthread_queue_work(&priv->disp_thread[crtc_id].worker,
> -			&vbl_ctrl->work);
> +	kthread_queue_work(&priv->disp_thread.worker, &vbl_ctrl->work);
>  
>  	return 0;
>  }
> @@ -284,14 +283,12 @@ static int msm_drm_uninit(struct device *dev)
>  		kfree(vbl_ev);
>  	}
>  
> +	kthread_flush_worker(&priv->disp_thread.worker);
> +	kthread_stop(priv->disp_thread.thread);

I realize this is moving existing code, but is there a race here? You can't have
work enqueued in between the flush and stop?

You might also want to use kthread_destroy_worker to do this work (in a
follow-up patch including the event threads too).

> +	priv->disp_thread.thread = NULL;
> +
>  	/* clean up display commit/event worker threads */

This comment needs updating now

>  	for (i = 0; i < priv->num_crtcs; i++) {
> -		if (priv->disp_thread[i].thread) {
> -			kthread_flush_worker(&priv->disp_thread[i].worker);
> -			kthread_stop(priv->disp_thread[i].thread);
> -			priv->disp_thread[i].thread = NULL;
> -		}
> -
>  		if (priv->event_thread[i].thread) {
>  			kthread_flush_worker(&priv->event_thread[i].worker);
>  			kthread_stop(priv->event_thread[i].thread);
> @@ -537,6 +534,22 @@ static int msm_drm_init(struct device *dev, struct drm_driver *drv)
>  	ddev->mode_config.funcs = &mode_config_funcs;
>  	ddev->mode_config.helper_private = &mode_config_helper_funcs;
>  
> +	/* initialize display thread */
> +	kthread_init_worker(&priv->disp_thread.worker);
> +	priv->disp_thread.dev = ddev;
> +	priv->disp_thread.thread = kthread_run(kthread_worker_fn,
> +					       &priv->disp_thread.worker,
> +					       "disp_thread");
> +	if (IS_ERR(priv->disp_thread.thread)) {
> +		DRM_DEV_ERROR(dev, "failed to create crtc_commit kthread\n");
> +		priv->disp_thread.thread = NULL;
> +		goto err_msm_uninit;
> +	}
> +
> +	ret = sched_setscheduler(priv->disp_thread.thread, SCHED_FIFO, &param);
> +	if (ret)
> +		pr_warn("display thread priority update failed: %d\n", ret);
> +
>  	/**
>  	 * this priority was found during empiric testing to have appropriate
>  	 * realtime scheduling to process display updates and interact with
> @@ -544,27 +557,6 @@ static int msm_drm_init(struct device *dev, struct drm_driver *drv)
>  	 */
>  	param.sched_priority = 16;
>  	for (i = 0; i < priv->num_crtcs; i++) {
> -
> -		/* initialize display thread */
> -		priv->disp_thread[i].crtc_id = priv->crtcs[i]->base.id;
> -		kthread_init_worker(&priv->disp_thread[i].worker);
> -		priv->disp_thread[i].dev = ddev;
> -		priv->disp_thread[i].thread =
> -			kthread_run(kthread_worker_fn,
> -				&priv->disp_thread[i].worker,
> -				"crtc_commit:%d", priv->disp_thread[i].crtc_id);
> -		if (IS_ERR(priv->disp_thread[i].thread)) {
> -			DRM_DEV_ERROR(dev, "failed to create crtc_commit kthread\n");
> -			priv->disp_thread[i].thread = NULL;
> -			goto err_msm_uninit;
> -		}
> -
> -		ret = sched_setscheduler(priv->disp_thread[i].thread,
> -					 SCHED_FIFO, &param);
> -		if (ret)
> -			dev_warn(dev, "disp_thread set priority failed: %d\n",
> -				 ret);
> -
>  		/* initialize event thread */
>  		priv->event_thread[i].crtc_id = priv->crtcs[i]->base.id;
>  		kthread_init_worker(&priv->event_thread[i].worker);
> diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
> index 9d11f32..e81b1fa 100644
> --- a/drivers/gpu/drm/msm/msm_drv.h
> +++ b/drivers/gpu/drm/msm/msm_drv.h
> @@ -197,7 +197,7 @@ struct msm_drm_private {
>  	unsigned int num_crtcs;
>  	struct drm_crtc *crtcs[MAX_CRTCS];
>  
> -	struct msm_drm_thread disp_thread[MAX_CRTCS];
> +	struct msm_drm_thread disp_thread;
>  	struct msm_drm_thread event_thread[MAX_CRTCS];
>  
>  	unsigned int num_encoders;
> -- 
> 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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