Re: [RFC PATCH v1] media: uvcvideo: Cache URB header data before processing

[Kieran Bingham]

Hi Keiichi,

On 24/07/18 05:18, Keiichi Watanabe wrote:
> Hi Kieran,
> 
> How is it going?
> I would appreciate if you could review this patch.

Thanks for the ping. ... This was on my todo list ... but just ... sooo
many Todo's :D

Ping bumped you to the top :)
And done.

Now to ping Laurent about my async patches :) <ping>

--
Regards

Kieran


> Best regards,
> Keiichi
> 
> On Thu, Jun 28, 2018 at 2:21 AM, Kieran Bingham
> <kieran.bingham@xxxxxxxxxxxxxxxx> wrote:
>> Hi Keiichi,
>>
>> I just wanted to reply here quickly to say this is a really interesting
>> development.
>>
>> I would like to review and test it properly; however I am now on holiday
>> until at least the 9th July and so I won't be able to look until after
>> that date.
>>
>> I didn't want you to be left hanging though :-)
>>
>> Ping me if you haven't heard anything by the 20th or so. Of course if
>> anyone else gets round to testing and reviewing then that's great too.
>>
>> Regards
>> --
>> Kieran
>>
>>
>>
>> On 27/06/18 11:34, Keiichi Watanabe wrote:
>>> On some platforms with non-coherent DMA (e.g. ARM), USB drivers use
>>> uncached memory allocation methods. In such situations, it sometimes
>>> takes a long time to access URB buffers.  This can be a cause of video
>>> flickering problems if a resolution is high and a USB controller has
>>> a very tight time limit. (e.g. dwc2) To avoid this problem, we copy
>>> header data from (uncached) URB buffer into (cached) local buffer.
>>>
>>> This change should make the elapsed time of the interrupt handler
>>> shorter on platforms with non-coherent DMA. We measured the elapsed
>>> time of each callback of uvc_video_complete without/with this patch
>>> while capturing Full HD video in
>>> https://webrtc.github.io/samples/src/content/getusermedia/resolution/.
>>> I tested it on the top of Kieran Bingham's Asynchronous UVC series
>>> https://www.mail-archive.com/linux-media@xxxxxxxxxxxxxxx/msg128359.html.
>>> The test device was Jerry Chromebook (RK3288) with Logitech Brio 4K.
>>> I collected data for 5 seconds. (There were around 480 callbacks in
>>> this case.) The following result shows that this patch makes
>>> uvc_video_complete about 2x faster.
>>>
>>>            | average | median  | min     | max     | standard deviation
>>> w/o caching| 45319ns | 40250ns | 33834ns | 142625ns| 16611ns
>>> w/  caching| 20620ns | 19250ns | 12250ns | 56583ns | 6285ns
>>>
>>> In addition, we confirmed that this patch doesn't make it worse on
>>> coherent DMA architecture by performing the same measurements on a
>>> Broadwell Chromebox with the same camera.
>>>
>>>            | average | median  | min     | max     | standard deviation
>>> w/o caching| 21026ns | 21424ns | 12263ns | 23956ns | 1932ns
>>> w/  caching| 20728ns | 20398ns |  8922ns | 45120ns | 3368ns
>>>
>>> Signed-off-by: Keiichi Watanabe <keiichiw@xxxxxxxxxxxx>
>>> ---
>>>
>>> After applying 6 patches in
>>> https://www.mail-archive.com/linux-media@xxxxxxxxxxxxxxx/msg128359.html,
>>> I measured elapsed time by adding the following code to
>>> /drivers/media/usb/uvc/uvc_video.c
>>>
>>> @@ -XXXX,6 +XXXX,9 @@ static void uvc_video_complete(struct urb *urb)
>>>         struct uvc_video_queue *queue = &stream->queue;
>>>       struct uvc_buffer *buf = NULL;
>>>       int ret;
>>> +     ktime_t start, end;
>>> +     int elapsed_time;
>>> +     start = ktime_get();
>>>       switch (urb->status) {
>>>       case 0:
>>>
>>> @@ -XXXX,6 +XXXX,10 @@ static void uvc_video_complete(struct urb *urb)
>>>
>>>       INIT_WORK(&uvc_urb->work, uvc_video_copy_data_work);
>>>       queue_work(stream->async_wq, &uvc_urb->work);
>>> +
>>> +     end = ktime_get();
>>> +     elapsed_time = ktime_to_ns(ktime_sub(end, start));
>>> +     pr_err("elapsed time: %d ns", elapsed_time);
>>>  }
>>>
>>>  /*
>>>
>>>
>>>  drivers/media/usb/uvc/uvc_video.c | 92 +++++++++++++++----------------
>>>  1 file changed, 43 insertions(+), 49 deletions(-)
>>> diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
>>> index a88b2e51a666..ff2eddc55530 100644
>>> --- a/drivers/media/usb/uvc/uvc_video.c
>>> +++ b/drivers/media/usb/uvc/uvc_video.c
>>> @@ -391,36 +391,15 @@ static inline ktime_t uvc_video_get_time(void)
>>>
>>>  static void
>>>  uvc_video_clock_decode(struct uvc_streaming *stream, struct uvc_buffer *buf,
>>> -                    const u8 *data, int len)
>>> +                    const u8 *data, int len, unsigned int header_size,
>>> +                    bool has_pts, bool has_scr)
>>>  {
>>>       struct uvc_clock_sample *sample;
>>> -     unsigned int header_size;
>>> -     bool has_pts = false;
>>> -     bool has_scr = false;
>>>       unsigned long flags;
>>>       ktime_t time;
>>>       u16 host_sof;
>>>       u16 dev_sof;
>>>
>>> -     switch (data[1] & (UVC_STREAM_PTS | UVC_STREAM_SCR)) {
>>> -     case UVC_STREAM_PTS | UVC_STREAM_SCR:
>>> -             header_size = 12;
>>> -             has_pts = true;
>>> -             has_scr = true;
>>> -             break;
>>> -     case UVC_STREAM_PTS:
>>> -             header_size = 6;
>>> -             has_pts = true;
>>> -             break;
>>> -     case UVC_STREAM_SCR:
>>> -             header_size = 8;
>>> -             has_scr = true;
>>> -             break;
>>> -     default:
>>> -             header_size = 2;
>>> -             break;
>>> -     }
>>> -
>>>       /* Check for invalid headers. */
>>>       if (len < header_size)
>>>               return;
>>> @@ -717,11 +696,10 @@ void uvc_video_clock_update(struct uvc_streaming *stream,
>>>   */
>>>
>>>  static void uvc_video_stats_decode(struct uvc_streaming *stream,
>>> -             const u8 *data, int len)
>>> +                                const u8 *data, int len,
>>> +                                unsigned int header_size, bool has_pts,
>>> +                                bool has_scr)
>>>  {
>>> -     unsigned int header_size;
>>> -     bool has_pts = false;
>>> -     bool has_scr = false;
>>>       u16 uninitialized_var(scr_sof);
>>>       u32 uninitialized_var(scr_stc);
>>>       u32 uninitialized_var(pts);
>>> @@ -730,25 +708,6 @@ static void uvc_video_stats_decode(struct uvc_streaming *stream,
>>>           stream->stats.frame.nb_packets == 0)
>>>               stream->stats.stream.start_ts = ktime_get();
>>>
>>> -     switch (data[1] & (UVC_STREAM_PTS | UVC_STREAM_SCR)) {
>>> -     case UVC_STREAM_PTS | UVC_STREAM_SCR:
>>> -             header_size = 12;
>>> -             has_pts = true;
>>> -             has_scr = true;
>>> -             break;
>>> -     case UVC_STREAM_PTS:
>>> -             header_size = 6;
>>> -             has_pts = true;
>>> -             break;
>>> -     case UVC_STREAM_SCR:
>>> -             header_size = 8;
>>> -             has_scr = true;
>>> -             break;
>>> -     default:
>>> -             header_size = 2;
>>> -             break;
>>> -     }
>>> -
>>>       /* Check for invalid headers. */
>>>       if (len < header_size || data[0] < header_size) {
>>>               stream->stats.frame.nb_invalid++;
>>> @@ -957,10 +916,41 @@ static void uvc_video_stats_stop(struct uvc_streaming *stream)
>>>   * to be called with a NULL buf parameter. uvc_video_decode_data and
>>>   * uvc_video_decode_end will never be called with a NULL buffer.
>>>   */
>>> +static void uvc_video_decode_header_size(const u8 *data, int *header_size,
>>> +                                      bool *has_pts, bool *has_scr)
>>> +{
>>> +     switch (data[1] & (UVC_STREAM_PTS | UVC_STREAM_SCR)) {
>>> +     case UVC_STREAM_PTS | UVC_STREAM_SCR:
>>> +             *header_size = 12;
>>> +             *has_pts = true;
>>> +             *has_scr = true;
>>> +             break;
>>> +     case UVC_STREAM_PTS:
>>> +             *header_size = 6;
>>> +             *has_pts = true;
>>> +             break;
>>> +     case UVC_STREAM_SCR:
>>> +             *header_size = 8;
>>> +             *has_scr = true;
>>> +             break;
>>> +     default:
>>> +             *header_size = 2;
>>> +     }
>>> +}
>>> +
>>>  static int uvc_video_decode_start(struct uvc_streaming *stream,
>>> -             struct uvc_buffer *buf, const u8 *data, int len)
>>> +                               struct uvc_buffer *buf, const u8 *urb_data,
>>> +                               int len)
>>>  {
>>>       u8 fid;
>>> +     u8 data[12];
>>> +     unsigned int header_size;
>>> +     bool has_pts = false, has_scr = false;
>>> +
>>> +     /* Cache the header since urb_data is uncached memory. The size of
>>> +      * header is at most 12 bytes.
>>> +      */
>>> +     memcpy(data, urb_data, min(len, 12));
>>>
>>>       /* Sanity checks:
>>>        * - packet must be at least 2 bytes long
>>> @@ -983,8 +973,12 @@ static int uvc_video_decode_start(struct uvc_streaming *stream,
>>>                       uvc_video_stats_update(stream);
>>>       }
>>>
>>> -     uvc_video_clock_decode(stream, buf, data, len);
>>> -     uvc_video_stats_decode(stream, data, len);
>>> +     uvc_video_decode_header_size(data, &header_size, &has_pts, &has_scr);
>>> +
>>> +     uvc_video_clock_decode(stream, buf, data, len, header_size, has_pts,
>>> +                            has_scr);
>>> +     uvc_video_stats_decode(stream, data, len, header_size, has_pts,
>>> +                            has_scr);
>>>
>>>       /* Store the payload FID bit and return immediately when the buffer is
>>>        * NULL.
>>> --
>>> 2.18.0.rc2.346.g013aa6912e-goog
>>>
>>
>> --
>> Regards
>> --
>> Kieran

-- 
Regards
--
Kieran