Re: [ANNOUNCE] Videobuf improvements to allow its usage with USB drivers

[Mauro Carvalho Chehab <mchehab@infradead.org>]

On Sun, 13 Apr 2008 18:17:54 +0200 (CEST)
Markus Rechberger <mrechberger@empiatech.com> wrote:

> >        Conclusion:
> 
> > The time consumption to receive the stream where reduced from about 33.38 seconds to 0.05 seconds
> 
> the question is moreover what made capture_example go
> up to 100% CPU in the first try and to 0% in the
> second one.
> I'm not sure about the old implementation in the
> original driver, although I'm just curious about the
> details here. xawtv usually uses very little cputime
> at all. 
> If I use 
> "$ time mplayer tv:// -tv driver=v4l2" it shows up 
> 
> real 0m40.972s
> user 0m0.230s
> sys  0m0.050s
> 
> your benchmark is a bit unclear.

The advantage of using capture_example for benchmark tests is that it is a very
simple mmap loop, without multi-thread, and just discarding the return. With
this, you're timing just the minimal requirements for receiving frames.

A TV application will also need to use the video adapter to present images, and
may do some other tasks, like running DSP algorithms for de-interlacing. It may
also discard frames, if there's not enough CPU to work will all of them. So,
you will never know how much of those times are due to V4L kernelspace part.

On the tests I did here with TV applications, the amount of performance,
reported by "top" also indicated that the previous approach were worse.

For example, on the same centino machine @1.5 GHZ, mplayer with "-tv driver=v4l2"
were ranging from 30% to 75% of CPU. With videobuf, the CPU consumption were
close to 23%, without much variation.

Cheers,
Mauro

--
video4linux-list mailing list
Unsubscribe mailto:video4linux-list-request@redhat.com?subject=unsubscribe
https://www.redhat.com/mailman/listinfo/video4linux-list