Hi Kieran,
Thank you for the patch.
On Friday, 12 January 2018 11:19:27 EET 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()
> ---
> drivers/media/usb/uvc/uvc_queue.c | 12 +++-
> drivers/media/usb/uvc/uvc_video.c | 116 +++++++++++++++++++++++++++----
> drivers/media/usb/uvc/uvcvideo.h | 24 ++++++-
> 3 files changed, 138 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/media/usb/uvc/uvc_queue.c
> b/drivers/media/usb/uvc/uvc_queue.c index 5a9987e547d3..598087eeb5c2 100644
> --- a/drivers/media/usb/uvc/uvc_queue.c
> +++ b/drivers/media/usb/uvc/uvc_queue.c
> @@ -179,10 +179,22 @@ static void uvc_stop_streaming(struct vb2_queue *vq)
> struct uvc_video_queue *queue = vb2_get_drv_priv(vq);
> struct uvc_streaming *stream = uvc_queue_to_stream(queue);
>
> + /* Prevent new buffers coming in. */
> + spin_lock_irq(&queue->irqlock);
> + queue->flags |= UVC_QUEUE_STOPPING;
> + spin_unlock_irq(&queue->irqlock);
> +
> + /*
> + * All pending work should be completed before disabling the stream, as
> + * all URBs will be free'd during uvc_video_enable(s, 0).
> + */
> + flush_workqueue(stream->async_wq);
> +
> uvc_video_enable(stream, 0);
>
> spin_lock_irq(&queue->irqlock);
> uvc_queue_return_buffers(queue, UVC_BUF_STATE_ERROR);
> + queue->flags &= ~UVC_QUEUE_STOPPING;
> spin_unlock_irq(&queue->irqlock);
As discussed today I believe you'll rework this part so I won't comment on it.
> }
>
> diff --git a/drivers/media/usb/uvc/uvc_video.c
> b/drivers/media/usb/uvc/uvc_video.c index 3878bec3276e..fb6b5af17380 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -1058,21 +1058,74 @@ static int uvc_video_decode_start(struct
> uvc_streaming *stream, return data[0];
> }
>
> -static void uvc_video_decode_data(struct uvc_streaming *stream,
> +static void uvc_video_copy_packets(struct uvc_urb *uvc_urb)
Maybe uvc_video_copy_data() as the function doesn't copy the full packets but
the data only ?
> +{
> + unsigned int i;
> +
> + 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);
> + }
> +}
> +
> +/*
> + * uvc_video_decode_data_work: Asynchronous memcpy processing
> + *
> + * Perform memcpy tasks in process context, with completion handlers
> + * to return the URB, and buffer handles.
> + *
> + * The work submitter must pre-determine that the work is safe
s/safe/safe./
Could you explain what safe work means ?
> + */
> +static void uvc_video_copy_data_work(struct work_struct *work)
> +{
> + struct uvc_urb *uvc_urb = container_of(work, struct uvc_urb, work);
> + struct uvc_streaming *stream = uvc_urb->stream;
> + struct uvc_video_queue *queue = &stream->queue;
> + int ret;
> +
> + uvc_video_copy_packets(uvc_urb);
> +
> + /*
> + * Prevent resubmitting URBs when shutting down to ensure that no new
> + * work item will be scheduled after uvc_stop_streaming() flushes the
> + * work queue.
> + */
> + spin_lock_irq(&queue->irqlock);
> + if (!(queue->flags & UVC_QUEUE_STOPPING)) {
> + ret = usb_submit_urb(uvc_urb->urb, GFP_ATOMIC);
> + if (ret < 0)
> + uvc_printk(KERN_ERR,
> + "Failed to resubmit video URB (%d).\n",
> + ret);
> + }
> + spin_unlock_irq(&queue->irqlock);
> +}
> +
> +static void uvc_video_decode_data(struct uvc_urb *uvc_urb,
> struct uvc_buffer *buf, const __u8 *data, int len)
> {
> - unsigned int maxlen, nbytes;
> - void *mem;
> + unsigned int active_op = uvc_urb->async_operations;
> + struct uvc_copy_op *decode = &uvc_urb->copy_operations[active_op];
> + unsigned int maxlen;
>
> if (len <= 0)
> return;
>
> - /* Copy the video data to the buffer. */
> maxlen = buf->length - buf->bytesused;
> - mem = buf->mem + buf->bytesused;
> - nbytes = min((unsigned int)len, maxlen);
> - memcpy(mem, data, nbytes);
> - buf->bytesused += nbytes;
> +
> + /* Take a buffer reference for async work */
> + kref_get(&buf->ref);
> +
> + decode->buf = buf;
> + decode->src = data;
> + decode->dst = buf->mem + buf->bytesused;
> + decode->len = min_t(unsigned int, len, maxlen);
> +
> + buf->bytesused += decode->len;
>
> /* Complete the current frame if the buffer size was exceeded. */
> if (len > maxlen) {
> @@ -1080,6 +1133,8 @@ static void uvc_video_decode_data(struct uvc_streaming
> *stream, buf->error = 1;
> buf->state = UVC_BUF_STATE_READY;
> }
> +
> + uvc_urb->async_operations++;
> }
>
> static void uvc_video_decode_end(struct uvc_streaming *stream,
> @@ -1187,7 +1242,7 @@ static void uvc_video_decode_isoc(struct uvc_urb
> *uvc_urb, continue;
>
> /* Decode the payload data. */
> - uvc_video_decode_data(stream, buf, mem + ret,
> + uvc_video_decode_data(uvc_urb, buf, mem + ret,
> urb->iso_frame_desc[i].actual_length - ret);
>
> /* Process the header again. */
> @@ -1248,9 +1303,9 @@ static void uvc_video_decode_bulk(struct uvc_urb
> *uvc_urb, * sure buf is never dereferenced if NULL.
> */
>
> - /* Process video data. */
> + /* Prepare video data for processing. */
> if (!stream->bulk.skip_payload && buf != NULL)
> - uvc_video_decode_data(stream, buf, mem, len);
> + uvc_video_decode_data(uvc_urb, buf, mem, len);
>
> /* Detect the payload end by a URB smaller than the maximum size (or
> * a payload size equal to the maximum) and process the header again.
> @@ -1322,6 +1377,7 @@ static void uvc_video_complete(struct urb *urb)
> struct uvc_streaming *stream = uvc_urb->stream;
> struct uvc_video_queue *queue = &stream->queue;
> struct uvc_buffer *buf = NULL;
> + unsigned long flags;
> int ret;
>
> switch (urb->status) {
> @@ -1344,12 +1400,39 @@ static void uvc_video_complete(struct urb *urb)
>
> buf = uvc_queue_get_current_buffer(queue);
>
> + /* Re-initialise the URB async work. */
> + uvc_urb->async_operations = 0;
> +
> + /*
> + * Process the URB headers, and optionally queue expensive memcpy tasks
> + * to be deferred to a work queue.
> + */
> stream->decode(uvc_urb, buf);
>
> - if ((ret = usb_submit_urb(urb, GFP_ATOMIC)) < 0) {
> - uvc_printk(KERN_ERR, "Failed to resubmit video URB (%d).\n",
> - ret);
> + /* Without any queued work, we must submit the URB. */
How about "If no async work is needed, resubmit the URB immediately." ?
> + if (!uvc_urb->async_operations) {
> + ret = usb_submit_urb(uvc_urb->urb, GFP_ATOMIC);
> + if (ret < 0)
> + uvc_printk(KERN_ERR,
> + "Failed to resubmit video URB (%d).\n",
> + ret);
> + return;
> + }
> +
> + /*
> + * When the stream is stopped, all URBs are freed as part of the call to
> + * uvc_stop_streaming() and must not be handled asynchronously. In that
> + * event we can safely complete the packet work directly in this
> + * context, without resubmitting the URB.
> + */
> + spin_lock_irqsave(&queue->irqlock, flags);
> + if (!(queue->flags & UVC_QUEUE_STOPPING)) {
> + INIT_WORK(&uvc_urb->work, uvc_video_copy_data_work);
> + queue_work(stream->async_wq, &uvc_urb->work);
> + } else {
> + uvc_video_copy_packets(uvc_urb);
> }
> + spin_unlock_irqrestore(&queue->irqlock, flags);
> }
>
> /*
> @@ -1620,6 +1703,11 @@ static int uvc_init_video(struct uvc_streaming
> *stream, gfp_t gfp_flags)
>
> uvc_video_stats_start(stream);
>
> + stream->async_wq = alloc_workqueue("uvcvideo", WQ_UNBOUND | WQ_HIGHPRI,
> + 0);
> + if (!stream->async_wq)
> + return -ENOMEM;
Shouldn't you call destroy_workqueue() somewhere ?
> if (intf->num_altsetting > 1) {
> struct usb_host_endpoint *best_ep = NULL;
> unsigned int best_psize = UINT_MAX;
> diff --git a/drivers/media/usb/uvc/uvcvideo.h
> b/drivers/media/usb/uvc/uvcvideo.h index 6a18dbfc3e5b..4a814da03913 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -411,6 +411,7 @@ struct uvc_buffer {
>
> #define UVC_QUEUE_DISCONNECTED (1 << 0)
> #define UVC_QUEUE_DROP_CORRUPTED (1 << 1)
> +#define UVC_QUEUE_STOPPING (1 << 2)
>
> struct uvc_video_queue {
> struct vb2_queue queue;
> @@ -483,12 +484,30 @@ struct uvc_stats_stream {
> };
>
> /**
> + * struct uvc_copy_op: Context structure to schedule asynchronous memcpy
> + *
> + * @buf: active buf object for this operation
> + * @dst: copy destination address
> + * @src: copy source address
> + * @len: copy length
> + */
> +struct uvc_copy_op {
> + struct uvc_buffer *buf;
> + void *dst;
> + const __u8 *src;
> + int len;
Can the length be negative ?
> +};
> +
> +/**
> * struct uvc_urb - URB context management structure
> *
> * @urb: the URB described by this context structure
> * @stream: UVC streaming context
> * @buffer: memory storage for the URB
> * @dma: DMA coherent addressing for the urb_buffer
> + * @async_operations: counter to indicate the number of copy operations
> + * @copy_operations: work descriptors for asynchronous copy operations
> + * @work: work queue entry for asynchronous decode
> */
> struct uvc_urb {
> struct urb *urb;
> @@ -496,6 +515,10 @@ struct uvc_urb {
>
> char *buffer;
> dma_addr_t dma;
> +
> + unsigned int async_operations;
> + struct uvc_copy_op copy_operations[UVC_MAX_PACKETS];
> + struct work_struct work;
> };
>
> struct uvc_streaming {
> @@ -528,6 +551,7 @@ struct uvc_streaming {
> /* Buffers queue. */
> unsigned int frozen : 1;
> struct uvc_video_queue queue;
> + struct workqueue_struct *async_wq;
> void (*decode)(struct uvc_urb *uvc_urb, struct uvc_buffer *buf);
>
> /* Context data used by the bulk completion handler. */
--
Regards,
Laurent Pinchart
