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    Subject[RFT PATCH v3 6/6] uvcvideo: Move decode processing to process context
    Date
    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@ideasonboard.com>

    ---
    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);
    }

    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)
    +{
    + 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
    + */
    +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. */
    + 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;
    +
    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;
    +};
    +
    +/**
    * 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. */
    --
    git-series 0.9.1
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      Last update: 2018-01-14 23:25    [W:3.840 / U:0.328 seconds]
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