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Date: Thu, 2 Dec 2004 13:22:18 +0100
From: Florian Schmidt <mista.tapas@gmx.net>
To: Ingo Molnar <mingo@elte.hu>
Cc: Rui Nuno Capela <rncbc@rncbc.org>, linux-kernel@vger.kernel.org,
       Lee Revell <rlrevell@joe-job.com>, mark_h_johnson@raytheon.com,
       "K.R. Foley" <kr@cybsft.com>, Bill Huey <bhuey@lnxw.com>,
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       Shane Shrybman <shrybman@aei.ca>, Amit Shah <amit.shah@codito.com>,
       Esben Nielsen <simlo@phys.au.dk>, Andrew Morton <akpm@osdl.org>
Subject: Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm3-V0.7.31-19
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On Thu, 2 Dec 2004 09:40:40 +0100
Ingo Molnar <mingo@elte.hu> wrote:

> > actually a single client doing nasty (non RT) stuff in its process()
> > callback can "starve" jackd. AFAIK jackd waits until the last client
> > has finished its process callback. So, if some client's process
> > callback decides to use (for example) some blocking system call (big
> > no no) and consequently falls asleep for a relatively long time, then
> > it can cause jackd to miss its deadline. I'm not sure though wether
> > this triggers an xrun in jackd or just a delay exceeded message.
> 
> since the period size in Rui's test is so small (-p64 is 1.6 msecs?),

ca. 1.3ms

> the 2.6 msec timeout in pipe_poll() already generates an xrun.

yep. now the question is: why did jackd have to wait so long for the
client? what was the client doing? was it sleeping? what client was it?
probably not the simple jack_test client, right?

Short tests ((20 minutes, due to lack of time) with cvs jackd and a
number of modified jack_test clients (added a for loop in the process()
callback to burn cycles to increase the cpu load) show no xruns here
even with relatively high cpu load (around 70%) and a periodsize of 64
frames. Of course i had the mandatory additional kernel compile running
in the background :)

flo

Oh wow. Just before hitting send i got three xruns of around
0.020-0.050msec. Ok, will read up on recent emails to see what to do to
debug these.