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Date: Thu, 2 Dec 2004 14:10:02 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Florian Schmidt <mista.tapas@gmx.net>
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>,
       Adam Heath <doogie@debian.org>, Thomas Gleixner <tglx@linutronix.de>,
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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
Message-ID: <20041202131002.GA30503@elte.hu>
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* Florian Schmidt <mista.tapas@gmx.net> wrote:

> Hmm, i wonder if there's a way to detect non RT behaviour in jackd
> clients. I mean AFAIK the only thing allowed for the process callback
> of on is the FIFO it waits on to be woken, right? Every other sleeping
> is to be considered a bug. 

there's such a feature in -RT kernels. If a user process calls:

	gettimeofday(1,1);

then the kernel turns 'atomic mode' on. To turn it off, call:

	gettimeofday(1,0);

while in atomic-mode, any non-atomic activity (scheduling) will produce
a kernel message and a SIGUSR2 sent to the offending process (once,
atomic mode has to be re-enabled again for the next message). Preemption
by a higher-prio task does not trigger a message/signal.

If you run the client under gdb you should be able to catch the SIGUSR2
signal and then you can see the offending code's backtrace via 'bt'.

	Ingo