[pulseaudio-discuss] [PATCH] Change the default fragment size to 5 ms

[David Henningsson]

On 2014-10-22 18:21, Alexander E. Patrakov wrote:
> Of course, this only applies to ALSA devices that can't use tsched, as
> well as to OSS on more exotic platforms.
>
> This is needed for compatibility with Wine games that use DirectSound8
> on distributions such as Arch Linux who don't accept the unofficial
> winepulse patch. The reason is that Wine DirectSound8 emulation requests
> a period of 10 ms and expects it to work for the purposes of timing. And
> in fact, it cannot know (via ALSA API) that it is not going to work!
>
> A known malware-free test application is Foobar2000 version 1.2. Later
> versions no longer use DirectSound.
>
> This issue is not going to be fixed on the Wine side, because the audio
> subsystem in Wine is not really maintained, and the maintainer has
> already privately expressed some negative thoughts about the state of
> the linux audio ecosystem in general.
>
> The correct solution (at least from the "isolate the clients from
> hardware limitations as thoroughly as possible" viewpoint) would be to
> consume audio from sink inputs using a timer if the actual sink does not
> provide sufficiently small minreq. In other words, adapt tsched to BATCH
> cards and drop non-tsched. But that's a whole project. So, as a stopgap
> solution for running Wine games on e.g. USB audio (which is a topic that
> pops up regularly on #pulseaudio IRC channel), let's reduce the default
> fragment size to a value suitable for unpatched Wine.
>
> Regarding the value: on my system, for mp3 playback through Foobar2000,
> 8ms fragments work, 9ms fragments result in constant underruns.
>
> Wine wiki recommends 5ms.
>
> On devices that can use tsched, there is no problem.

On Ubuntu, since before my time, this has been the default:

default-fragments = 8
default-fragment-size-msec = 10

...so 8 x 10 = 80 ms. If you end up with 5 x 4 = 20 ms, I think that's a 
bit too short/sensitive, we should then increase the number of periods 
to 16 or at least 8 in the same go, so you'll end up with something 
above 50 ms in total. I think this could help against underruns caused 
by inoptimal scheduling.

I discussed this with Alexander briefly on Linuxcon, and I'm not opposed 
to lowering the fragment-size parameter. I have not looked into the wine 
DirectSound driver, but if it requires a period size of 10 ms, why does 
not 10 ms work?

Also, how well does wine work with non-ALSA sinks, such as bluetooth, 
tunnel sinks, etc?




>
> Signed-off-by: Alexander E. Patrakov <patrakov at gmail.com>
> ---
>   man/pulse-daemon.conf.5.xml.in | 4 ++--
>   src/daemon/daemon-conf.c       | 2 +-
>   src/daemon/daemon.conf.in      | 2 +-
>   3 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/man/pulse-daemon.conf.5.xml.in b/man/pulse-daemon.conf.5.xml.in
> index 8bd076d..ff54435 100644
> --- a/man/pulse-daemon.conf.5.xml.in
> +++ b/man/pulse-daemon.conf.5.xml.in
> @@ -463,8 +463,8 @@ USA.
>       </option>
>       <option>
>         <p><opt>default-fragment-size-msec=</opt>The duration of a
> -      single fragment. Defaults to 25ms (i.e. the total buffer is thus
> -      100ms long).</p>
> +      single fragment. Defaults to 5ms (i.e. the total buffer is thus
> +      20ms long).</p>
>       </option>
>
>     </section>
> diff --git a/src/daemon/daemon-conf.c b/src/daemon/daemon-conf.c
> index b7a85aa..6dc15cf 100644
> --- a/src/daemon/daemon-conf.c
> +++ b/src/daemon/daemon-conf.c
> @@ -96,7 +96,7 @@ static const pa_daemon_conf default_conf = {
>       .lock_memory = false,
>       .deferred_volume = true,
>       .default_n_fragments = 4,
> -    .default_fragment_size_msec = 25,
> +    .default_fragment_size_msec = 5,
>       .deferred_volume_safety_margin_usec = 8000,
>       .deferred_volume_extra_delay_usec = 0,
>       .default_sample_spec = { .format = PA_SAMPLE_S16NE, .rate = 44100, .channels = 2 },
> diff --git a/src/daemon/daemon.conf.in b/src/daemon/daemon.conf.in
> index 5b20130..3d758cd 100644
> --- a/src/daemon/daemon.conf.in
> +++ b/src/daemon/daemon.conf.in
> @@ -85,7 +85,7 @@ ifelse(@HAVE_SYS_RESOURCE_H@, 1, [dnl
>   ; default-channel-map = front-left,front-right
>
>   ; default-fragments = 4
> -; default-fragment-size-msec = 25
> +; default-fragment-size-msec = 5
>
>   ; enable-deferred-volume = yes
>   ; deferred-volume-safety-margin-usec = 8000
>

-- 
David Henningsson, Canonical Ltd.
https://launchpad.net/~diwic