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Subject[RFC/RFT PATCH 6/6] uvcvideo: Move decode processing to process context
Date
From: Kieran Bingham <kieran.bingham@ideasonboard.com>

Newer high definition cameras, and cameras with multiple lenses such as
the range of stereovision 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>
---
drivers/media/usb/uvc/uvc_queue.c | 12 +++-
drivers/media/usb/uvc/uvc_video.c | 114 ++++++++++++++++++++++++++-----
drivers/media/usb/uvc/uvcvideo.h | 24 +++++++-
3 files changed, 132 insertions(+), 18 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_queue.c b/drivers/media/usb/uvc/uvc_queue.c
index 204dd91a8526..07fcbfc132c9 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 045ac655313c..b7b32a6bc2dc 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -1058,21 +1058,70 @@ static int uvc_video_decode_start(struct uvc_streaming *stream,
return data[0];
}

-static void uvc_video_decode_data(struct uvc_streaming *stream,
- struct uvc_buffer *buf, const __u8 *data, int len)
+/*
+ * 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_decode_data_work(struct work_struct *work)
{
- unsigned int maxlen, nbytes;
- void *mem;
+ 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;
+ unsigned int i;
+ bool stopping;
+ int ret;
+
+ for (i = 0; i < uvc_urb->packets; i++) {
+ struct uvc_decode_op *op = &uvc_urb->decodes[i];
+
+ memcpy(op->dst, op->src, op->len);
+
+ /* Release reference taken on this buffer */
+ uvc_queue_buffer_release(op->buf);
+ }
+
+ /*
+ * 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);
+ stopping = queue->flags & UVC_QUEUE_STOPPING;
+ spin_unlock_irq(&queue->irqlock);
+
+ if (stopping)
+ return;
+
+ 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_decode_op *decode,
+ struct uvc_urb *uvc_urb, struct uvc_buffer *buf,
+ const __u8 *data, int len)
+{
+ 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 +1129,8 @@ static void uvc_video_decode_data(struct uvc_streaming *stream,
buf->error = 1;
buf->state = UVC_BUF_STATE_READY;
}
+
+ uvc_urb->packets++;
}

static void uvc_video_decode_end(struct uvc_streaming *stream,
@@ -1162,6 +1213,8 @@ static void uvc_video_decode_isoc(struct uvc_urb *uvc_urb,
int ret, i;

for (i = 0; i < urb->number_of_packets; ++i) {
+ struct uvc_decode_op *op = &uvc_urb->decodes[uvc_urb->packets];
+
if (urb->iso_frame_desc[i].status < 0) {
uvc_trace(UVC_TRACE_FRAME, "USB isochronous frame "
"lost (%d).\n", urb->iso_frame_desc[i].status);
@@ -1187,7 +1240,7 @@ 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(op, uvc_urb, buf, mem + ret,
urb->iso_frame_desc[i].actual_length - ret);

/* Process the header again. */
@@ -1248,9 +1301,12 @@ static void uvc_video_decode_bulk(struct uvc_urb *uvc_urb,
* sure buf is never dereferenced if NULL.
*/

- /* Process video data. */
- if (!stream->bulk.skip_payload && buf != NULL)
- uvc_video_decode_data(stream, buf, mem, len);
+ /* Prepare video data for processing. */
+ if (!stream->bulk.skip_payload && buf != NULL) {
+ struct uvc_decode_op *op = &uvc_urb->decodes[0];
+
+ uvc_video_decode_data(op, 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.
@@ -1322,7 +1378,8 @@ 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;
- int ret;
+ unsigned long flags;
+ bool stopping;

switch (urb->status) {
case 0:
@@ -1342,14 +1399,30 @@ static void uvc_video_complete(struct urb *urb)
return;
}

+ /*
+ * Simply accept and discard completed URBs without processing when the
+ * stream is being shutdown. URBs will be freed as part of the
+ * uvc_video_enable(s, 0) action, so we must not queue asynchronous
+ * work based upon them.
+ */
+ spin_lock_irqsave(&queue->irqlock, flags);
+ stopping = queue->flags & UVC_QUEUE_STOPPING;
+ spin_unlock_irqrestore(&queue->irqlock, flags);
+
+ if (stopping)
+ return;
+
buf = uvc_queue_get_current_buffer(queue);

+ /* Re-initialise the URB packet work */
+ uvc_urb->packets = 0;
+
+ /* Process the URB headers, but work is 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);
- }
+ /* Handle any heavy lifting required */
+ INIT_WORK(&uvc_urb->work, uvc_video_decode_data_work);
+ queue_work(stream->async_wq, &uvc_urb->work);
}

/*
@@ -1621,6 +1694,11 @@ 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 2e51bbdf5dac..1f7399cb66e1 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_decode_op: Context structure to schedule asynchronous memcpy
+ *
+ * @buf: active buf object for this decode
+ * @dst: copy destination address
+ * @src: copy source address
+ * @len: copy length
+ */
+struct uvc_decode_op {
+ struct uvc_buffer *buf;
+ void *dst;
+ const __u8 *src;
+ int len;
+};
+
+/**
* struct uvc_urb - URB context management structure
*
* @urb: described URB. Must be allocated with usb_alloc_urb()
* @stream: UVC streaming context
* @urb_buffer: memory storage for the URB
* @urb_dma: DMA coherent addressing for the urb_buffer
+ * @packets: counter to indicate the number of copy operations
+ * @decodes: 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 *urb_buffer;
dma_addr_t urb_dma;
+
+ unsigned int packets;
+ struct uvc_decode_op decodes[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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