[alsa-devel] [PATCH - AAF PCM plugin 0/7] Follow-up improvements

[Takashi Iwai]

On Mon, 10 Dec 2018 11:22:01 +0100,
Takashi Iwai wrote:
> 
> On Sat, 08 Dec 2018 02:55:43 +0100,
> Andre Guedes wrote:
> > 
> > Hi all,
> > 
> > This patch series provides some follow-up improvements to the AVTP Audio
> > Format (AAF) plugin. The highlight of this series is the implementation of
> > a transmission offload mechanism which improves the plugin performance
> > considerably. Details are provided in the following paragraphs.
> > 
> > Currently, the AVTPDU transmission interval is controlled by the AAF plugin, in
> > software. At every timer expiration, the plugin transmits one AVTPDU.  This has
> > some implications in terms of task scheduling. For instance, in class A
> > streams, AVTPDUs are transmitted at every 125 us which means the application
> > task should be scheduled-in at every 125 us. In a general purpose Linux system,
> > such scheduling interval can be hard to cope with in the long-run.
> > 
> > To mitigate that issue, this series introduces a transmission offload mechanism
> > that leverages the SO_TXTIME sockopt and ETF qdisc features recently introduced
> > to kernel 4.19. Instead of sending one AVTPDU at every timer expiration, the
> > plugin sends several AVTPDUs at once to the kernel, configuring their Tx time
> > so the transmission interval is maintained. The kernel can then offload packet
> > transmission to the hardware (if the network controller supports it), providing
> > more transmission time accuracy.  This offloading mechanism enables the
> > application to sleep for longer times, easing on task scheduling.  
> > 
> > To illustrate the improvements provided by this series, I ran a before-after
> > experiment. The experiment setup consisted in 2 PCs with Intel i210 card
> > connected back-to-back running an up-to-date Archlinux with kernel 4.19.4.  I
> > ran 'aplay' for 5 minutes on one PC and captured the AVTPDUs on the other PC.
> > The metric under evaluation is the transmission interval and it is measured by
> > checking the 'time_delta' information from ethernet frames captured at the
> > receiving side. If you're interested in reproducing the experiments, let me
> > know and I can share my helper scripts.
> > 
> > The table below shows the experiment outcome for a Class A, stereo, 16-bit
> > sample, 48 kHz stream. The unit is nanoseconds.
> > 
> >        |   Mean |   Stdev |     Min |     Max |   Range |
> > -------+--------+---------+---------+---------+---------+
> > Before | 125000 |    1154 |   75311 |  172144 |   96833 |
> > After  | 125000 |      18 |  124960 |  125048 |      88 |
> > 
> > 
> > Before this patchset, the transmission interval mean is equal to the optimal
> > value (Class A stream -> 125 us interval), and it is kept the same after the
> > patchset. However, the dispersion measurements had improved considerably,
> > meaning the system is consistently transmitting AVTPDUs at the correct
> > interval.
> > 
> > Finally, to help the review process, here follows a quick summary of the
> > patches within this series:
> > 	* PATCH 1: fixes a type in the plugin documentation.
> > 	* PATCH 2: enables the user to configure the presentation time
> > 	  tolerance.
> > 	* PATCH 3-5: refactor the code in order to land the offload mechanism
> > 	  code smoothly.
> > 	* PATCH 6-7: implement the transmission offload mechanism.
> > 
> > This series can also be found in my alsa-plugins tree in github [1].
> > 
> > Regards,
> > 
> > Andre
> > 
> > [1] https://github.com/aguedes/alsa-plugins
> > 
> > Andre Guedes (7):
> >   doc: Fix typo in AAF doc
> >   aaf: Add presentation time tolerance
> >   aaf: Refactor AVTPDU transmission routines
> >   aaf: Refactor AVTPDU reception routines
> >   aaf: Refactor timeout routines
> >   aaf: Tx multiple AVTPDUs per media clock tick
> >   aaf: AVTPDU transmission periodicity
> 
> Applied all patches now.  Thanks.

BTW, while building libavtp for 32bit x86, the unit test failed:
The build log is found at
  https://build.opensuse.org/package/live_build_log/home:tiwai/libavtp/openSUSE_Factory/i586

x86_64 seems working, so it must be specific to 32bit arch.


Takashi