On 06/11/2018 22:58, Laurent Pinchart wrote:
> Hi Kieran,
>
> Thank you for the patch.
>
> On Tuesday, 6 November 2018 23:27:17 EET Kieran Bingham wrote:
>> From: Kieran Bingham <[email protected]>
>>
>> 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 <[email protected]>
>
> Reviewed-by: Laurent Pinchart <[email protected]>
>
> 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.
Possibly - lets keep it in mind for when we get back to looking at
Keiichi's patch and any cache management for further performance
improvements
--
Kieran
>
>> ---
>> 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;
>
>
