Hi Guennadi,
Thank you for reviewing / taking a look through the series.
On 04/06/18 13:09, Guennadi Liakhovetski wrote:
> 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?
I think you're right.
This could very likely be changed to GFP_KERNEL.
Does this series impact anything on your async-controls series ?
--
Kieran
>
>> + if (ret < 0)
>> + uvc_printk(KERN_ERR, "Failed to resubmit video URB (%d).\n",
>> + ret);
>> +}
>
> [snip]
>
> Thannks
> Guennadi
>
