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From: Arnd Bergmann <arnd@arndb.de>
To: linuxppc-dev@lists.ozlabs.org
Subject: Re: Floating point in the kernel
Date: Thu, 10 Dec 2009 22:35:47 +0100
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Cc: linuxppc-dev <linuxppc-dev@ozlabs.org>,
	Sean MacLennan <smaclennan@pikatech.com>
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On Thursday 10 December 2009, Sean MacLennan wrote:
> To be honest, I can't find why we are scheduling :( They only way we
> give up the CPU is with locking... and none of the locks where hit
> during the problem. We also never get near our timeslice... the longest
> run I saw when the problem happened was 670us. 
> 
> Is there a way to disable scheduling? We currently do not have preempt
> enabled... but may in the future.

If you do preempt_disable(), it should give you a nice oops with a backtrace
at the point where an actual schedule happens.

The sequence should be something like

preempt_disable();
enable_kernel_fp();
/* use FP here */
preempt_enable();
/* may schedule again */

	Arnd <><