On Sat, 18 Feb 2023 13:15:49 -0800
Rob Clark <robdclark@xxxxxxxxx> wrote:
> From: Rob Clark <robdclark@xxxxxxxxxxxx>
>
> Allow userspace to use the EPOLLPRI/POLLPRI flag to indicate an urgent
> wait (as opposed to a "housekeeping" wait to know when to cleanup after
> some work has completed). Usermode components of GPU driver stacks
> often poll() on fence fd's to know when it is safe to do things like
> free or reuse a buffer, but they can also poll() on a fence fd when
> waiting to read back results from the GPU. The EPOLLPRI/POLLPRI flag
> lets the kernel differentiate these two cases.
>
> Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
Hi,
where would the UAPI documentation of this go?
It seems to be missing.
If a Wayland compositor is polling application fences to know which
client buffer to use in its rendering, should the compositor poll with
PRI or not? If a compositor polls with PRI, then all fences from all
applications would always be PRI. Would that be harmful somehow or
would it be beneficial?
Thanks,
pq
> ---
> drivers/dma-buf/sync_file.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
> index fb6ca1032885..c30b2085ee0a 100644
> --- a/drivers/dma-buf/sync_file.c
> +++ b/drivers/dma-buf/sync_file.c
> @@ -192,6 +192,14 @@ static __poll_t sync_file_poll(struct file *file, poll_table *wait)
> {
> struct sync_file *sync_file = file->private_data;
>
> + /*
> + * The POLLPRI/EPOLLPRI flag can be used to signal that
> + * userspace wants the fence to signal ASAP, express this
> + * as an immediate deadline.
> + */
> + if (poll_requested_events(wait) & EPOLLPRI)
> + dma_fence_set_deadline(sync_file->fence, ktime_get());
> +
> poll_wait(file, &sync_file->wq, wait);
>
> if (list_empty(&sync_file->cb.node) &&
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