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Re: Resolution to republish MSP as a note

From: Chris Rogers <crogers@google.com>
Date: Wed, 8 Aug 2012 10:21:52 -0700
Message-ID: <CA+EzO0m882dmcHFeak-376FLw-ihxhfRSnmvQm9=-kL5m=kigQ@mail.gmail.com>
To: Jussi Kalliokoski <jussi.kalliokoski@gmail.com>
Cc: Stéphane Letz <letz@grame.fr>, public-audio@w3.org
On Wed, Aug 8, 2012 at 7:35 AM, Jussi Kalliokoski <
jussi.kalliokoski@gmail.com> wrote:

> On Wed, Aug 8, 2012 at 4:25 PM, Stéphane Letz <letz@grame.fr> wrote:
>> >
>> > I'm probably badly misinformed, but the value of high priority threads
>> seems a bit vague to me, since I'm not sure about what's the OS support
>> level for high-priority threads, I think for example in Linux you still
>> have to compile your own kernel to get real high priority thread support.
>> No. You would possibly need a special kernel for very ¨*low latency*
>> thread scheduling, but not for RT scheduling and thread priority
>> management. A regular Linux kernel is now quite usable, assuming the audio
>> thread can take RT scheduling capability, which is given using Realtime Kit
>> in PulseAudio AFAICS or correctly setting a special "realtime" group with
>> appropriate values (see here for JACK:
>> http://jackaudio.org/realtime_vs_realtime_kernel and
>> http://jackaudio.org/linux_rt_config)
> Thought I'd be misinformed! Thanks for the clarification, and sorry for
> the mixup.
>> On OSX real-time threads are actually "time constraints" threads, that
>> are going to preempt any other non RT thread and are "interleaved" with
>> other RT threads. The CoreAudio callback will run in a real-time
>> constraints started and configurated by the CoreAudio frameworks for the
>> audio application.
>> > And using high-priority threads might not always even be desirable, for
>> example in low-end devices it'd be horrible if the UI became completely
>> unusable because an audio thread was occupying the whole thread.
>> But if not RT, then the audio will "glitch"... Do we want reliable audio?
>> or not?
> I think you mean to ask "do we want audio in RT threads", because even
> that doesn't always warrant reliable audio nor does not having it exclude
> reliable audio. The answer to that question would be sometimes yes,
> sometimes not. Glitchless audio isn't worth much if the application becomes
> otherwise completely unusable. Is high-priority audio threads a feature
> that warrants for the complexity that comes with the native nodes?
> Especially given that we still have the possibility of RT thread workers
> open.
> I'm pretty sure that for example my Android phone doesn't run it's audio
> in a real-time thread, even networking connections can sometimes glitch the
> audio. But it's never bothered me, I'd actually rather have the UI in an RT
> thread like iOS does and have that always go before the audio and anything
> else for that matter. I'm pretty sure I'm not the only one.

But many people have asked for improvements to the Android audio
performance and do not appreciate high-latency and glitches.  I know that
iOS *does* use high-priority threads and it works great for them, so your
argument seems to be rather weak.  Believe it or not, I think there will
actually be many people who are interested to process live audio in
real-time in web applications, or to play synthesizers using the MIDI API.
 Just because we've had terrible performance on the web with Flash, etc.
doesn't mean we have to stay in the stone age, lagging so far behind the
desktop audio applications abilities.


> Cheers,
> Jussi
Received on Wednesday, 8 August 2012 17:22:21 UTC

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