linux-kernel - SCHED_FIFO & system()

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Date:	Thu, 17 Jan 2008 11:19:07 +0100 (CET)
From:	linux@...dmangroup.com
To:	linux-kernel@...r.kernel.org
Subject: SCHED_FIFO & system()

Hello,
I have some strange behavior in one of my systems.

I have a real-time kernel thread under SCHED_FIFO which is running every
10ms.
It is blocking on a semaphore and released by a timer interrupt every 10ms.
Generally this works really well.

However, there is a module in the system that makes a / system() / call
from c-code in user-space;

  system("run_my_script");

By calling and running a bash script. Independent of how the actual
script looks like the real time kernel thread does not get scheduled under
the time of 80ms -- the time it takes for the system() call to finish.

I can see when running a LTT session that the wake_up event occurs for
the real time thread 10ms into the system call but nevertheless the real
time kernel thread does not get scheduled.

The thread that calls system("run_my_script") is configured as SCHED_OTHER.

The Kernel is 2.6.21.

Anybody who recognize this or similar situations?

Cheers // Matias
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