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Subject[PATCH v4 6/6] media: 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()

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);
+ 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 *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) {
@@ -1064,6 +1097,8 @@ 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,
@@ -1272,7 +1307,7 @@ 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. */
@@ -1334,9 +1369,9 @@ 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.
@@ -1422,7 +1457,7 @@ 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 */
@@ -1436,6 +1471,9 @@ 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;
+
if (vb2_qmeta) {
spin_lock_irqsave(&qmeta->irqlock, flags);
if (!list_empty(&qmeta->irqqueue))
@@ -1444,12 +1482,24 @@ static void uvc_video_complete(struct urb *urb)
spin_unlock_irqrestore(&qmeta->irqlock, flags);
}

+ /*
+ * 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;
}
+
+ INIT_WORK(&uvc_urb->work, uvc_video_copy_data_work);
+ queue_work(stream->async_wq, &uvc_urb->work);
}

/*
@@ -1544,25 +1594,29 @@ 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;
}

if (free_buffers)
uvc_free_urb_buffers(stream);
+
+ destroy_workqueue(stream->async_wq);
}

/*
@@ -1720,6 +1774,11 @@ 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 112eed49bf50..27c230430eda 100644
--- a/drivers/media/usb/uvc/uvcvideo.h
+++ b/drivers/media/usb/uvc/uvcvideo.h
@@ -485,12 +485,30 @@ 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;
@@ -498,6 +516,10 @@ 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 {
@@ -530,6 +552,7 @@ 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);

@@ -583,6 +606,11 @@ 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 {
struct usb_device *udev;
struct usb_interface *intf;
--
git-series 0.9.1
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