linux-kernel - Re: CONFIG_PEEMPT_RT_FULL vs. CONFIG_PREEMPT

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Date:	Mon, 15 Aug 2011 22:44:36 +0200
From:	Remy Bohmer <linux@...mer.net>
To:	Tim Sander <tim.sander@....com>
Cc:	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ibm.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: CONFIG_PEEMPT_RT_FULL vs. CONFIG_PREEMPT_RTB

Hi,

> Besides of the cpu load i also found out that with rt11 i can again wake up
> usermode from a IRQF_NO_THREAD waiting on a waitqueue. So the steps outlined
> in this mail http://www.spinics.net/lists/linux-rt-users/msg06834.html do not
> seem to be neccessary anymore? Or does this create an error and than some high
> load?

Try running with CONFIG_DEBUG_SPINLOCK_SLEEP and you would probably
see some errors...

If you have CONFIG_PREEMPT_RT_FULL set, then the __wake_up function of
the waitqueue runs into a spinlock. This spinlock will be converted to
a mutex since it is a regular spinlock, not a raw_spinlock. A
mutex-lock might sleep. Calling sleeping functions from hard-irq
context is illegal.

Kind regards,

Remy
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