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

Daniel Vetter
2022-03-17T09:59:13Z

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