Hi Kieran,
I've got a question:
On Tue, 27 Mar 2018, Kieran Bingham wrote:
> Newer high definition cameras, and cameras with multiple lenses such as
> the range of stereo-vision cameras now available have ever increasing
> data rates.
>
> The inclusion of a variable length packet header in URB packets mean
> that we must memcpy the frame data out to our destination 'manually'.
> This can result in data rates of up to 2 gigabits per second being
> processed.
>
> To improve efficiency, and maximise throughput, handle the URB decode
> processing through a work queue to move it from interrupt context, and
> allow multiple processors to work on URBs in parallel.
>
> Signed-off-by: Kieran Bingham <kieran.bingham@xxxxxxxxxxxxxxxx>
>
> ---
> v2:
> - Lock full critical section of usb_submit_urb()
>
> v3:
> - Fix race on submitting uvc_video_decode_data_work() to work queue.
> - Rename uvc_decode_op -> uvc_copy_op (Generic to encode/decode)
> - Rename decodes -> copy_operations
> - Don't queue work if there is no async task
> - obtain copy op structure directly in uvc_video_decode_data()
> - uvc_video_decode_data_work() -> uvc_video_copy_data_work()
>
> v4:
> - Provide for_each_uvc_urb()
> - Simplify fix for shutdown race to flush queue before freeing URBs
> - Rebase to v4.16-rc4 (linux-media/master) adjusting for metadata
> conflicts.
>
> drivers/media/usb/uvc/uvc_video.c | 107 ++++++++++++++++++++++++-------
> drivers/media/usb/uvc/uvcvideo.h | 28 ++++++++-
> 2 files changed, 111 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> index 7dd0dcb457f3..a62e8caf367c 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -1042,21 +1042,54 @@ static int uvc_video_decode_start(struct uvc_streaming *stream,
> return data[0];
> }
>
> -static void uvc_video_decode_data(struct uvc_streaming *stream,
> +/*
> + * uvc_video_decode_data_work: Asynchronous memcpy processing
> + *
> + * Perform memcpy tasks in process context, with completion handlers
> + * to return the URB, and buffer handles.
> + */
> +static void uvc_video_copy_data_work(struct work_struct *work)
> +{
> + struct uvc_urb *uvc_urb = container_of(work, struct uvc_urb, work);
> + unsigned int i;
> + int ret;
> +
> + for (i = 0; i < uvc_urb->async_operations; i++) {
> + struct uvc_copy_op *op = &uvc_urb->copy_operations[i];
> +
> + memcpy(op->dst, op->src, op->len);
> +
> + /* Release reference taken on this buffer */
> + uvc_queue_buffer_release(op->buf);
> + }
> +
> + ret = usb_submit_urb(uvc_urb->urb, GFP_ATOMIC);
Does this still have to be ATOMIC now that it's called from a work queue
context?
> + if (ret < 0)
> + uvc_printk(KERN_ERR, "Failed to resubmit video URB (%d).\n",
> + ret);
> +}
[snip]
Thannks
Guennadi
