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

Matthew Brost
2022-03-17T15:08:12Z

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
> >>
>