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

[Sean Paul <sean@poorly.run>]

On Thu, Nov 08, 2018 at 02:23:33PM -0800, Jeykumar Sankaran wrote:
> On 2018-11-01 12:09, Sean Paul wrote:
> > 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?
> I looked further into this comment. Ideally, we call into msm_unbind only
> when
> the device is released and we release the device only on the last close of
> the drm device. So the userspace doesn't have any device handle to make
> ioctl calls, which could queue jobs to this queue. Since we are making sure
> to flush out the last job already on the queue, we can safely call the
> kthread_stop here.

Cool, thanks for digging into this!

Sean

> 
> Thanks and Regards,
> Jeykumar S.
> 
> > 
> > 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
> > > 
> > > _______________________________________________
> > > Freedreno mailing list
> > > Freedreno@lists.freedesktop.org
> > > https://lists.freedesktop.org/mailman/listinfo/freedreno
> 
> -- 
> Jeykumar S

-- 
Sean Paul, Software Engineer, Google / Chromium OS
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