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. Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
