Can GStreamer plugin perform DMA copy

[GStreamer-devel mailing list]

Hi,

Currently I have constructed a custom element that separate one video source
to 2 video.
For example, one 800x1200 video separate to two 800x600 video.
I use memcpy method to copy video data to 2 new GstBuffer and then push it
to src pad.
So it costs much more cpu usage.

I further check the tee element, which also branch a new pipeline, a new
GstBuffer and low cpu usage.
But I could not find what I want, it seems using gst_pad_push_list(), I
didn't find out where it copies the data.

Could someone give any example or reference for the DMA copy?
Many thanks.




--
Sent from: http://gstreamer-devel.966125.n4.nabble.com/
_______________________________________________
gstreamer-devel mailing list
[hidden email]
https://lists.freedesktop.org/mailman/listinfo/gstreamer-devel

[GStreamer-devel mailing list]

That depends on what you want to do. If the buffers you push to
downstream will not be changed, then you can just add ref to the
Gstbuffer and no need to copy it. If they will be changed/written, you
need to do the copy. The GstAllocator has a mem_copy function to let
you provide your own memcpy function for GstMemory. It will be called
when the GstBuffer really needs a copy.



On Mon, 2021-05-31 at 06:58 -0500, ChrisLiuv via gstreamer-devel wrote:

> Hi,
>
> Currently I have constructed a custom element that separate one video
> source
> to 2 video.
> For example, one 800x1200 video separate to two 800x600 video.
> I use memcpy method to copy video data to 2 new GstBuffer and then
> push it
> to src pad.
> So it costs much more cpu usage.
>
> I further check the tee element, which also branch a new pipeline, a
> new
> GstBuffer and low cpu usage.
> But I could not find what I want, it seems using gst_pad_push_list(),
> I
> didn't find out where it copies the data.
>
> Could someone give any example or reference for the DMA copy?
> Many thanks.
>
>
>
>
> --
> Sent from: http://gstreamer-devel.966125.n4.nabble.com/
> _______________________________________________
> gstreamer-devel mailing list
> [hidden email]
> https://lists.freedesktop.org/mailman/listinfo/gstreamer-devel

_______________________________________________
gstreamer-devel mailing list
[hidden email]
https://lists.freedesktop.org/mailman/listinfo/gstreamer-devel

[GStreamer-devel mailing list]

El lunes, 31 de mayo de 2021 13:58:32 (CEST) ChrisLiuv via gstreamer-devel
escribió:

> Currently I have constructed a custom element that separate one video source
> to 2 video.
> For example, one 800x1200 video separate to two 800x600 video.
> I use memcpy method to copy video data to 2 new GstBuffer and then push it
> to src pad.
> So it costs much more cpu usage.
>
> I further check the tee element, which also branch a new pipeline, a new
> GstBuffer and low cpu usage.
> But I could not find what I want, it seems using gst_pad_push_list(), I
> didn't find out where it copies the data.

Looking at the loop where gst_tee_handle_data() iterates over all the pads[1]
and to the code that actually pushes the buffers[2], it looks like the
original GstBuffer isn't actually copied, just having its reference count
increased (because it's going to be used from each of the downstream pipeline
branches) and pushed to all the pads.

So, apparently, it's effectively the same buffer. If you add probes on each of
the downstream branches, you should see that the same GstBuffer* pointer
values appears on all the branches.

Cheers.

[1] https://gitlab.freedesktop.org/gstreamer/gstreamer/blob/master/plugins/
elements/gsttee.c#L941
[2] https://gitlab.freedesktop.org/gstreamer/gstreamer/blob/master/plugins/
elements/gsttee.c#L856

--
Enrique Ocaña


_______________________________________________
gstreamer-devel mailing list
[hidden email]
https://lists.freedesktop.org/mailman/listinfo/gstreamer-devel

[GStreamer-devel mailing list]

Hi,

Thanks for your reply.
My video data is form 2 image sensor, and is line interleaved, so I need to
deinterleave it first.

The  gstdmabuf.html
<https://gstreamer.freedesktop.org/documentation/allocators/gstdmabuf.html?gi-language=c>  
only explains allocate and check, don't know the difference between
gstallocator.html
<https://gstreamer.freedesktop.org/documentation/gstreamer/gstallocator.html?gi-language=c>  

Seems that I need to implement it myself?

I searched the current gst-plugin-good, only v4l2 uses
gst_dmabuf_allocator_new ();
sys/v4l2/gstv4l2bufferpool.c:517:      pool->allocator =
gst_dmabuf_allocator_new ();
I'll further check how it work.

Any suggestions would be greatly appreciated.

Thanks.




--
Sent from: http://gstreamer-devel.966125.n4.nabble.com/
_______________________________________________
gstreamer-devel mailing list
[hidden email]
https://lists.freedesktop.org/mailman/listinfo/gstreamer-devel