Re: [PATCH 2/3] drm/msm/gpu: Park scheduler threads for system suspend

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Mar 10, 2022 at 03:46:05PM -0800, Rob Clark wrote:
> From: Rob Clark <robdclark@chromium.org>
> 
> In the system suspend path, we don't want to be racing with the
> scheduler kthreads pushing additional queued up jobs to the hw
> queue (ringbuffer).  So park them first.  While we are at it,
> move the wait for active jobs to complete into the new system-
> suspend path.
> 
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> ---
>  drivers/gpu/drm/msm/adreno/adreno_device.c | 68 ++++++++++++++++++++--
>  1 file changed, 64 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/adreno/adreno_device.c b/drivers/gpu/drm/msm/adreno/adreno_device.c
> index 8859834b51b8..0440a98988fc 100644
> --- a/drivers/gpu/drm/msm/adreno/adreno_device.c
> +++ b/drivers/gpu/drm/msm/adreno/adreno_device.c
> @@ -619,22 +619,82 @@ static int active_submits(struct msm_gpu *gpu)
>  static int adreno_runtime_suspend(struct device *dev)
>  {
>  	struct msm_gpu *gpu = dev_to_gpu(dev);
> -	int remaining;
> +
> +	/*
> +	 * We should be holding a runpm ref, which will prevent
> +	 * runtime suspend.  In the system suspend path, we've
> +	 * already waited for active jobs to complete.
> +	 */
> +	WARN_ON_ONCE(gpu->active_submits);
> +
> +	return gpu->funcs->pm_suspend(gpu);
> +}
> +
> +static void suspend_scheduler(struct msm_gpu *gpu)
> +{
> +	int i;
> +
> +	/*
> +	 * Shut down the scheduler before we force suspend, so that
> +	 * suspend isn't racing with scheduler kthread feeding us
> +	 * more work.
> +	 *
> +	 * Note, we just want to park the thread, and let any jobs
> +	 * that are already on the hw queue complete normally, as
> +	 * opposed to the drm_sched_stop() path used for handling
> +	 * faulting/timed-out jobs.  We can't really cancel any jobs
> +	 * already on the hw queue without racing with the GPU.
> +	 */
> +	for (i = 0; i < gpu->nr_rings; i++) {
> +		struct drm_gpu_scheduler *sched = &gpu->rb[i]->sched;
> +		kthread_park(sched->thread);

Shouldn't we have some proper interfaces for this? Also I'm kinda
wondering how other drivers do this, feels like we should have a standard
way.

Finally not flushing out all in-flight requests sounds a bit like a bad
idea for system suspend/resume since that's also the hibernation path, and
that would mean your shrinker/page reclaim stops working. At least in full
generality. Which ain't good for hibernation.

Adding Christian and Andrey.
-Daniel

> +	}
> +}
> +
> +static void resume_scheduler(struct msm_gpu *gpu)
> +{
> +	int i;
> +
> +	for (i = 0; i < gpu->nr_rings; i++) {
> +		struct drm_gpu_scheduler *sched = &gpu->rb[i]->sched;
> +		kthread_unpark(sched->thread);
> +	}
> +}
> +
> +static int adreno_system_suspend(struct device *dev)
> +{
> +	struct msm_gpu *gpu = dev_to_gpu(dev);
> +	int remaining, ret;
> +
> +	suspend_scheduler(gpu);
>  
>  	remaining = wait_event_timeout(gpu->retire_event,
>  				       active_submits(gpu) == 0,
>  				       msecs_to_jiffies(1000));
>  	if (remaining == 0) {
>  		dev_err(dev, "Timeout waiting for GPU to suspend\n");
> -		return -EBUSY;
> +		ret = -EBUSY;
> +		goto out;
>  	}
>  
> -	return gpu->funcs->pm_suspend(gpu);
> +	ret = pm_runtime_force_suspend(dev);
> +out:
> +	if (ret)
> +		resume_scheduler(gpu);
> +
> +	return ret;
>  }
> +
> +static int adreno_system_resume(struct device *dev)
> +{
> +	resume_scheduler(dev_to_gpu(dev));
> +	return pm_runtime_force_resume(dev);
> +}
> +
>  #endif
>  
>  static const struct dev_pm_ops adreno_pm_ops = {
> -	SET_SYSTEM_SLEEP_PM_OPS(pm_runtime_force_suspend, pm_runtime_force_resume)
> +	SET_SYSTEM_SLEEP_PM_OPS(adreno_system_suspend, adreno_system_resume)
>  	SET_RUNTIME_PM_OPS(adreno_runtime_suspend, adreno_runtime_resume, NULL)
>  };
>  
> -- 
> 2.35.1
> 

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