Re: [Jack-Devel] Jack 0.120 incorrect error recovery for -n 3

On Sun, Apr 17, 2011 at 01:33:50PM +0000, Fons Adriaensen wrote:
> On Sun, Apr 17, 2011 at 10:48:04AM +0000, Fons Adriaensen wrote:
>  
> > > So it randomly siwtches between 2 and 3 ?
> > 
> > It more or less alternates between the two, with
> > some random element being involved as well.
> > 
> > As posted before, what happens is that after a
> > subgraph timeout (which is reported) sometimes
> > the alsa device is restarted (as it should be),
> > and sometimes (when in the '-n 3' state) it
> > isn't. Since in the same cycle there was no
> > driver->write() (as the result of the timeout),
> > things continue to work but with a period shift
> > between playback and capture, as if '-n 2'. 
> > When a new timeout occurs in that state it will
> > trigger a stop/start, restoring the original
> > conditions. So the net result is that the system
> > almost alternates between the two states.
> 
> I found out a bit more.
> 
> 1. It seems the ALSA device restart is triggered by
> an error condition in alsa_driver_wait() and not
> by the engine.
> 
> 2. OTOH the engine, when there is subgraph timeout,
> (in this case due to an app not closing down cleanly)
> will not call driver->write() for the current cycle. 
> 
> With -n 3, (2) can happen without (1), as as far as
> ALSA is concerned there is no problem - it still has
> almost a complete period before anything overruns.
> 
> Now to keep things in sync either each cycle must be
> completed fully, including writing to the ALSA device,
> or the device must be restarted. This really should
> be enforced 'by design' but it isn't.
> 
> There seem to be two solutions: 
> 
> A. Make sure the ALSA device is restarted when the
> engine does not complete the cycle. This would 
> negate any advantage there is to using -n 3, the
> whole point of it is that an occasional single cycle
> taking a bit too long is not fatal.
> 
> B. Always complete the cycle by calling driver-write().

B is the right thing to do, will look into it this evening.
i dont remember, why i have changed this.


> 
> 
> Ciao,
> 
> -- 
> FA
> 
> 
> 
> 
> 
> 
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-- 
torben Hohn

1303135901.23184_0.ltw:2,a <20110418141106.GA13755 at siel dot b>