Hi Kieran,
Thank you for the patch.
On Tuesday, 6 November 2018 23:27:17 EET Kieran Bingham wrote:
> From: Kieran Bingham <kieran.bingham@xxxxxxxxxxxxxxxx>
>
> 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>
Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
I wonder if we shouldn't, as a future improvement, only queue async work when
the quantity of data to be copied is above a certain threshold.
> ---
> 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.
>
> v5:
> - Rebase to media/v4.20-2
> - Use GFP_KERNEL allocation in uvc_video_copy_data_work()
> - Fix function documentation for uvc_video_copy_data_work()
> - Add periods to the end of sentences
> - Rename 'decode' variable to 'op' in uvc_video_decode_data()
> - Move uvc_urb->async_operations initialisation to before use
> - Move async workqueue to match uvc_streaming lifetime instead of
> streamon/streamoff
>
> drivers/media/usb/uvc/uvc_driver.c | 2 +-
> drivers/media/usb/uvc/uvc_video.c | 110 +++++++++++++++++++++++-------
> drivers/media/usb/uvc/uvcvideo.h | 28 ++++++++-
> 3 files changed, 116 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/media/usb/uvc/uvc_driver.c
> b/drivers/media/usb/uvc/uvc_driver.c index bc369a0934a3..e61a6d26e812
> 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -1883,6 +1883,8 @@ static void uvc_unregister_video(struct uvc_device
> *dev) video_unregister_device(&stream->vdev);
> video_unregister_device(&stream->meta.vdev);
>
> + destroy_workqueue(stream->async_wq);
> +
> uvc_debugfs_cleanup_stream(stream);
> }
> }
> diff --git a/drivers/media/usb/uvc/uvc_video.c
> b/drivers/media/usb/uvc/uvc_video.c index 7a7779e1b466..ce9e40444507 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -1094,21 +1094,54 @@ 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
> + *
> + * Copy URB data to video buffers in process context, releasing buffer
> + * references and requeuing the URB when done.
> + */
> +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_KERNEL);
> + if (ret < 0)
> + uvc_printk(KERN_ERR, "Failed to resubmit video URB (%d).\n",
> + ret);
> +}
> +
> +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 *op = &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);
> +
> + op->buf = buf;
> + op->src = data;
> + op->dst = buf->mem + buf->bytesused;
> + op->len = min_t(unsigned int, len, maxlen);
> +
> + buf->bytesused += op->len;
>
> /* Complete the current frame if the buffer size was exceeded. */
> if (len > maxlen) {
> @@ -1116,6 +1149,8 @@ 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,
> @@ -1324,7 +1359,7 @@ static void uvc_video_decode_isoc(struct uvc_urb
> *uvc_urb, uvc_video_decode_meta(stream, meta_buf, mem, ret);
>
> /* 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. */
> @@ -1384,9 +1419,9 @@ 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.
> @@ -1472,7 +1507,7 @@ static void uvc_video_complete(struct urb *urb)
> uvc_printk(KERN_WARNING, "Non-zero status (%d) in video "
> "completion handler.\n", urb->status);
> /* fall through */
> - case -ENOENT: /* usb_kill_urb() called. */
> + case -ENOENT: /* usb_poison_urb() called. */
> if (stream->frozen)
> return;
> /* fall through */
> @@ -1494,12 +1529,26 @@ static void uvc_video_complete(struct urb *urb)
> spin_unlock_irqrestore(&qmeta->irqlock, flags);
> }
>
> + /* 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, buf_meta);
>
> - if ((ret = usb_submit_urb(urb, GFP_ATOMIC)) < 0) {
> - uvc_printk(KERN_ERR, "Failed to resubmit video URB (%d).\n",
> - ret);
> + /* 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;
> }
> +
> + queue_work(stream->async_wq, &uvc_urb->work);
> }
>
> /*
> @@ -1594,20 +1643,22 @@ static int uvc_alloc_urb_buffers(struct
> uvc_streaming *stream, */
> static void uvc_uninit_video(struct uvc_streaming *stream, int
> free_buffers) {
> - struct urb *urb;
> - unsigned int i;
> + struct uvc_urb *uvc_urb;
>
> uvc_video_stats_stop(stream);
>
> - for (i = 0; i < UVC_URBS; ++i) {
> - struct uvc_urb *uvc_urb = &stream->uvc_urb[i];
> + /*
> + * We must poison the URBs rather than kill them to ensure that even
> + * after the completion handler returns, any asynchronous workqueues
> + * will be prevented from resubmitting the URBs.
> + */
> + for_each_uvc_urb(uvc_urb, stream)
> + usb_poison_urb(uvc_urb->urb);
>
> - urb = uvc_urb->urb;
> - if (urb == NULL)
> - continue;
> + flush_workqueue(stream->async_wq);
>
> - usb_kill_urb(urb);
> - usb_free_urb(urb);
> + for_each_uvc_urb(uvc_urb, stream) {
> + usb_free_urb(uvc_urb->urb);
> uvc_urb->urb = NULL;
> }
>
> @@ -1932,6 +1983,7 @@ int uvc_video_init(struct uvc_streaming *stream)
> struct uvc_streaming_control *probe = &stream->ctrl;
> struct uvc_format *format = NULL;
> struct uvc_frame *frame = NULL;
> + struct uvc_urb *uvc_urb;
> unsigned int i;
> int ret;
>
> @@ -2017,6 +2069,16 @@ int uvc_video_init(struct uvc_streaming *stream)
> }
> }
>
> + /* Allocate a stream specific work queue for asynchronous tasks. */
> + stream->async_wq = alloc_workqueue("uvcvideo", WQ_UNBOUND | WQ_HIGHPRI,
> + 0);
> + if (!stream->async_wq)
> + return -ENOMEM;
> +
> + /* Prepare asynchronous work items. */
> + for_each_uvc_urb(uvc_urb, stream)
> + INIT_WORK(&uvc_urb->work, uvc_video_copy_data_work);
> +
> return 0;
> }
>
> diff --git a/drivers/media/usb/uvc/uvcvideo.h
> b/drivers/media/usb/uvc/uvcvideo.h index 1bc17da7f3d4..0953e2e59a79 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -491,12 +491,30 @@ struct uvc_stats_stream {
> #define UVC_METATADA_BUF_SIZE 1024
>
> /**
> + * 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;
> + size_t 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;
> @@ -504,6 +522,10 @@ 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 {
> @@ -536,6 +558,7 @@ 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,
> struct uvc_buffer *meta_buf);
>
> @@ -589,6 +612,11 @@ struct uvc_streaming {
> } clock;
> };
>
> +#define for_each_uvc_urb(uvc_urb, uvc_streaming) \
> + for ((uvc_urb) = &(uvc_streaming)->uvc_urb[0]; \
> + (uvc_urb) < &(uvc_streaming)->uvc_urb[UVC_URBS]; \
> + ++(uvc_urb))
> +
> struct uvc_device_info {
> u32 quirks;
> u32 meta_format;
--
Regards,
Laurent Pinchart
