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

[Matthew Brost <matthew.brost@intel.com>]

On Thu, Mar 17, 2022 at 03:06:18AM -0700, Christian König wrote:
> Am 17.03.22 um 10:59 schrieb Daniel Vetter:
> > 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?
> 
> If I'm not completely mistaken we already should have one, yes.
> 
> > 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.
> 
> Completely agree, that looks like an incorrect workaround to me.
> 
> During suspend all userspace applications should be frozen and all f 
> their hardware activity flushed out and waited for completion.
>

Isn't that what Rob is doing?

He kills the scheduler preventing any new job from being submitted then
waits for an outstanding jobs to complete naturally complete (see the
wait_event_timeout below). If the jobs don't naturally complete the
suspend seems to be aborted? That flow makes sense to me and seems like
a novel way to avoid races.

Matt 
 
> I do remember that our internal guys came up with pretty much the same 
> idea and it sounded broken to me back then as well.
> 
> Regards,
> Christian.
> 
> >
> > 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
> >>
>