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SubjectRe: [PATCH 2/3] drm/atomic: Use kthread worker for nonblocking commits
On Sat, Sep 19, 2020 at 12:37:25PM -0700, Rob Clark wrote:
> From: Rob Clark <robdclark@chromium.org>
>
> This will allow us to more easily switch scheduling rules based on what
> userspace wants.
>
> Signed-off-by: Rob Clark <robdclark@chromium.org>

I still think switching to the highpriority systemwq as a start (like i915
already does) would be a good first step no matter what we end up doing
for the android thing.
-Daniel

> ---
> drivers/gpu/drm/drm_atomic_helper.c | 13 ++++++++----
> include/drm/drm_atomic.h | 31 +++++++++++++++++++++++++++++
> 2 files changed, 40 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 9e1ad493e689..75eeec5e7b10 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1659,11 +1659,11 @@ static void commit_tail(struct drm_atomic_state *old_state)
> drm_atomic_state_put(old_state);
> }
>
> -static void commit_work(struct work_struct *work)
> +static void commit_work(struct kthread_work *work)
> {
> struct drm_atomic_state *state = container_of(work,
> struct drm_atomic_state,
> - commit_work);
> + commit_kwork);
> commit_tail(state);
> }
>
> @@ -1797,6 +1797,7 @@ int drm_atomic_helper_commit(struct drm_device *dev,
> struct drm_atomic_state *state,
> bool nonblock)
> {
> + struct kthread_worker *worker = NULL;
> int ret;
>
> if (state->async_update) {
> @@ -1814,7 +1815,7 @@ int drm_atomic_helper_commit(struct drm_device *dev,
> if (ret)
> return ret;
>
> - INIT_WORK(&state->commit_work, commit_work);
> + kthread_init_work(&state->commit_kwork, commit_work);
>
> ret = drm_atomic_helper_prepare_planes(dev, state);
> if (ret)
> @@ -1857,8 +1858,12 @@ int drm_atomic_helper_commit(struct drm_device *dev,
> */
>
> drm_atomic_state_get(state);
> +
> if (nonblock)
> - queue_work(system_unbound_wq, &state->commit_work);
> + worker = drm_atomic_pick_worker(state);
> +
> + if (worker)
> + kthread_queue_work(worker, &state->commit_kwork);
> else
> commit_tail(state);
>
> diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h
> index d07c851d255b..8d0ee19953df 100644
> --- a/include/drm/drm_atomic.h
> +++ b/include/drm/drm_atomic.h
> @@ -373,8 +373,18 @@ struct drm_atomic_state {
> *
> * Work item which can be used by the driver or helpers to execute the
> * commit without blocking.
> + *
> + * This is deprecated, use commit_kwork.
> */
> struct work_struct commit_work;
> +
> + /**
> + * @commit_kwork:
> + *
> + * Work item which can be used by the driver or helpers to execute the
> + * commit without blocking.
> + */
> + struct kthread_work commit_kwork;
> };
>
> void __drm_crtc_commit_free(struct kref *kref);
> @@ -954,6 +964,27 @@ void drm_state_dump(struct drm_device *dev, struct drm_printer *p);
> (new_obj_state) = (__state)->private_objs[__i].new_state, 1); \
> (__i)++)
>
> +/**
> + * drm_atomic_pick_worker - helper to get kworker to use for nonblocking commit
> + * @state: the &drm_atomic_state for the commit
> + *
> + * Pick an appropriate worker for a given atomic update. The first CRTC
> + * invovled in the atomic update is used to pick the worker, to prevent
> + * serializing multiple pageflips / atomic-updates on indenpendent CRTCs.
> + */
> +static inline struct kthread_worker *
> +drm_atomic_pick_worker(const struct drm_atomic_state *state)
> +{
> + struct drm_crtc_state *crtc_state;
> + struct drm_crtc *crtc;
> + unsigned i;
> +
> + for_each_new_crtc_in_state(state, crtc, crtc_state, i)
> + return crtc->worker;
> +
> + return NULL;
> +}
> +
> /**
> * drm_atomic_crtc_needs_modeset - compute combined modeset need
> * @state: &drm_crtc_state for the CRTC
> --
> 2.26.2
>

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

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