[Bug 796721] New: queues: Should influence the number of allocated buffers when possible

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=796721

            Bug ID: 796721
           Summary: queues: Should influence the number of allocated
                    buffers when possible
    Classification: Platform
           Product: GStreamer
           Version: git master
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: gstreamer (core)
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: nicolas at ndufresne.ca
        QA Contact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---

As of now, queues completely ignore the allocation query. Though, for sized
queue to work properly, you need enough buffers to be allocated. So far, most
of the time this worked because the buffers pools can grow, or dynamic
allocation is being used. In this bug report, I'm suggesting that queues, when
they are configured with size in number of buffers, should influence the
allocation query to ensure that they are useful and that their thread does not
cause contention or starvation. Here's an example of starvation cause by queues
(requires a driver that do not implement VIDIOC_CREATE_BUFS):

gst-launch-1.0 v4l2src device=/dev/video1 ! queue min-threshold-buffers=10 !
glimagesink sync=0

p.s. This case should also try and increase the latency, worked around using
sync=0 here.

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