diff mbox series

[v7,06/15] dma-buf/sync_file: Support (E)POLLPRI

Message ID 20230227193535.2822389-7-robdclark@gmail.com (mailing list archive)
State Not Applicable
Headers
Series dma-fence: Deadline awareness |

Commit Message

Rob Clark Feb. 27, 2023, 7:35 p.m. UTC 
  From: Rob Clark <robdclark@chromium.org>

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@chromium.org>
---
 drivers/dma-buf/sync_file.c | 8 ++++++++
 1 file changed, 8 insertions(+)

Comments

Pekka Paalanen Feb. 28, 2023, 9:22 a.m. UTC | #1 
On Mon, 27 Feb 2023 11:35:12 -0800
Rob Clark <robdclark@gmail.com> wrote:

> From: Rob Clark <robdclark@chromium.org>
> 
> 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@chromium.org>
> ---
>  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 418021cfb87c..cbe96295373b 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());

Hi,

I don't think this doc will appear anywhere where it could be found,
maybe not in kernel HTML doc at all?

I also think this is not a good idea, but not my call.


Thanks,
pq


> +
>  	poll_wait(file, &sync_file->wq, wait);
>  
>  	if (list_empty(&sync_file->cb.node) &&
diff mbox series

Patch

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index 418021cfb87c..cbe96295373b 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) &&