Marco -- many thanks for your reply -- I've taken the liberty of CC'ing this informative reply to the Linux-Audio-Developers list (your CC was not posted as you're not a subscriber: http://lists.linuxaudio.org/pipermail/linux-audio-dev/2010-December/thread.… ). The list comprises a good number of people with expertise in both pulseaudio; hopefully the Jack sound server authors, including Paul Davis, will be willing to publicly share their perspectives on the issues raised regarding the role of pulseaudio on a handset and Linux audio performance/latency/efficiency issues. Here's a link to Marco's original post to meego-handset mailing list, forwarded below: http://lists.meego.com/pipermail/meego-handset/2010-December/000090.html ---------- Forwarded message ---------- From: Marco Ballesio <gibrovacco> Date: Sat, Dec 18, 2010 at 4:42 AM Subject: Re: Meego pulseaudio "compliance" and "enforcement" (was Re: [Meego-handset] Enabling Speakerphone) To: Niels Mayer <nielsmayer> Cc: meego-handset(a)lists.meego.com, Linux Audio Developers &lt;linux-audio-dev(a)lists.linuxaudio.org&gt; [...] Hi, sorry for the late reply but, whew, this was really long, definitely more than what my poor brain can handle in a single bunch ;). Maybe we could split this into a "Resource Policy Framework" and "Pulseaudio on Embedded" couple of threads. As a general comment on PA, it may appear odd but when I started working with it I shared 100% of your considerations. Working with it (not ON it), I started realising that, ok, it may not be perfect (and which software actually is?) but it brings definitely more benefits than troubles to the system. See my notes below for more details. ..snip.. Maybe you've read in some other of my posts here and there, I'm trying to get a Resource Policy Framework wiki somewhere. In the meanwhile, documents are scarce but present: - The MeeGo conference presentation: http://conference2010.meego.com/session/policy-framework-flexible-way-orche… Does not say too much, but it comes with some slides and many "mmmmh" (keepalive signals). - The resource policy application developer's manual: http://wiki.meego.com/images/Meego-policy-framework-developer-guide.pdf Mysteriously, it's not linked or referred to anywhere.. at least, now it's on this thread. - The source code: it may twist more than one nose but, at the end, I always like to check in the sources before/after Googling. Documents may be obsolete (who knows?) or expose a partial view. Code can't ;). Not that I want to say with this that we don't need more documents about the Resource Policy Framework... My pointers of above may begin to satiate your hunger (appetisers?). Unfortunately, this is still in the "dark side" of the documentation, which is currently application-centric. Hopefully one day we'll have an "Adaptation developer's guide", in the meanwhile, a good starting point may be checking the sources, the N900/Meego ruleset and posting questions here. If it's not enough, we may set up an IRC channel (if there's enough interest)... See my notes above about the project wiki. Your pointers are definitely good hints, thanks. this project covers the audio-specific cases: for what I understood it might very well be used as an ALSA enforcement point in the Framework so, more than compete with Resource Policy it would be complementary in case you don't really want/need to use a sound server. BTW, I could not find so much info, maybe you can help me to retrieve: - more than just source-code to describe how it works. - the developer's documentation for the appropriate layer to use, etc. - something like: http://wiki.maemo.org/Documentation/Maemo_5_Developer_Guide/Architecture/Mu… ..snip.. now, the pulseaudio cases. First of all, please note I'm not the best advocate for it, btw my 0.05 €. Posting some extracts of your comments to the PA mailing list will definitely give you a better insight for the internals of the server. And actually "elegant" was not referred to pulseaudio, but to the way its ports can handle audio routing instead of using ALSA (they bring better synchronisation). Yes, the sound server has shown instabilities in some cases and I personally used to uninstall it on my Ubuntu box immediately after the upgrades. Recently but many improvements have been made at a point that, on a PC, I'm nowadays not seeing it anymore jumping to a steady 30% of the CPU or completely jamming any audio output in the middle of a movie. Another _personal_ feeling I had is that pulseaudio was pretty hard to configure for a generic HW (like distros tend to do), but works pretty well after being tuned for a given one (like 95% of embedded products are). Very often the root issue may have been a wrong configuration for your system. I can agree from a kernel/ALSA pov (everything in userland appears to be less efficient than any kernel drivers ;) ), I strongly disagree from the system architecture's one. Some points you should consider: - Audio outputs frequency tuning: in the real word a crappy speaker costs less than a good one (strange?) so, unless you've a very high target price, you'll usually have to take the maximum out of garbage by "massaging" the output spectrum in order to get an adequate overall transfer function. And this must work with all of the applications -even the ones coming from third parties on which you don't have the bare minimum control on- and different analog outputs (front, rear, bt, ...). Not that pulseaudio comes with these features out-of-the-box, but it's quite easy to plug them in. - Audio inputs: the dual of audio outputs. - Mixing: it's possible that users will want more than one application accessing the audio output at the same time (e.g. navigator and car radio) or that they'll want to switch bw two different applications all of a sudden (e.g. radio and ringtone). In all these cases they'll want a good mixing and no sudden power steps when the ringtone app does not know about the volume level used for the radio. - Acoustic delay estimation: sitting in the middle of pulseaudio (running as a real-time thread) it's easier to write a proper AEC. Back to 2004 I've tried to grant, with a TI aic31, constant latencies for both LEC and AEC by just using ALSA and the application... It took a really long time to work. - It may not appear so, but it's energy-efficient (see my comments below if you just jumped out of your chair). Now, I don't mean that those things can be handled only by pulseaudio. Actually developers could write their own sound server, or use an already available one, to do all of this, but.. - How long would it take to be better than pulseaudio? (e.g. wrt my points above). - Can it grant the same solid user base and portability across embedded HW? - Could it grant the same level of contribution from companies with solid experience on the subject? - Are there architectural flaws for which pulseaudio couldn't effectively handle these cases? If yes, has anybody tried to discuss about them on the PA mailing list? I've no religious issues against jack and actually I don't have that much experience with it, so I'd like to know more about jack on embedded. I'd like to know, for instance, how many embedded, low-power devices are already using it and with which degree of success. Also it would be great to know if anybody has interfaced it with a cellular modem to handle Circuit-switched cellular calls, and if the device has actually been certified for such a service in any countries. please correct me if I'm wrong, but if I understood well most of the apps using _exclusively_ jack are aimed to audio/video composition/editing. Now, as we are on the IVI ML I think it's quite a strange use case (even though I must admit I don't know which requirements you have). see below (and above). well, it runs as real-time priority, so it's executed when it's scheduled. Context switches would not be different for any process (e.g. jack) running with the same scheduling. funnily, this is EXACTLY the same thing I thought the first time I profiled pulseaudio on the N900, then I found some reasonable explanation (scroll a little below). ..snip.. Yes, this is a bad aspect, but it's actually possible to change the output bitrate of the server (it depends on the port used). Maybe you could query on the PA mailing list for more knowledge on the subject. so we'll end up writing our own sound server or using a different one, won't we? As an alternative, we may have to heavily modify ALSA to suit our needs, and we'll not have yet covered all of the needed features. Personally, I would not say that MultiMedia with MeeGo on the N900 is already at the same quality of Maemo 5. Lots of tuning is imho still missing. You must consider that here there many algorithms involved that users/applications don't even know about, like the spectrum optimisations I've been mentioning before. If you could run an oprofile session over your tests you'd see that the actual CPU attributable to PA is pretty lower than your figures. ..snip.. As written above, PA is not only resampling and mixing here.. imho if the user/the developer didn't have to adjust the system to work with PA in order to achieve this, it's a success. The CPU usage comes from the fact we're actually running something we need. Sure it would, but with a lower set of features (and an higher cost for the audio system). It's up to the device price target/customer's pockets and needs to decide what's better. I would agree in some cases, that is when the system conditions don't require it to run multi-application use cases and the price tag for the audio system is irrelevant wrt the audio quality. Note for the reader: if you've reached this point it means you're really interested about pulseaudio on embedded devices :D. Regards