[gst-devel] Help needed to reduce unusually high CPU utilization in v4l2src, caused by memory copy.

[Yiliang Bao]

Hi Gibro,

Thanks for the kind reply. Even I remove the memcpy in v4l2src, the overhead
is still there. I guess the overhead is just shifted to another stage that
consumes the data. I found the problem was with the coherent buffer used in
the driver, since the v4l2 driver I am investigating uses the buffer queue
defined in videobuf-dma-contig.c. After I replace the coherent buffers with
streaming buffers, the problem goes away.

One correction to my previous email. The memory should "contiguous" instead
of "contingent"

Best regards,
Yiliang

On Fri, Jan 22, 2010 at 11:48 PM, Gibro Vacco <gibrovacco at gmail.com> wrote:

> Hi,
>
> would it ber possible to mmap the memory are from the driver so that
> v4l2src passes that very buffer to the remaining of the pipeline?
>
> The only problem would be that, in case of a circular buffer in the
> driver, each memory area will remain locked until the pipeline has
> ended processing it.
>
> On Thu, Jan 21, 2010 at 12:57 AM, yiliang <yiliangb at gmail.com> wrote:
> >
> > Hi,
> >
> > I am optimizing a V4L2 driver for video capture device. In the v4l2
> driver,
> > the DMA is performed based on frames using contingent memory buffers.
> After
> > a frame is captured, the frame data is copied to a application buffer in
> > v4l2src.
> >
> > gst_v4l2src_grab_frame()
> >  ->     *buf = gst_buffer_copy (pool_buffer);
> >
> > However, the time spent on copying the buffer is very costly, about 0.01
> > seconds, which is very large considering frame time is only 0.033
> seconds.
> >
> > I do not know whether this is the right forum. Any suggestions will be
> > appreciated.
> >
> > Thanks,
> > Yiliang
> >
> > --
> > View this message in context:
> http://n4.nabble.com/Help-needed-to-reduce-unusually-high-CPU-utilization-in-v4l2src-caused-by-memory-copy-tp1019508p1019508.html
> > Sent from the GStreamer-devel mailing list archive at Nabble.com.
> >
> >
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