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Date: Sun, 29 Sep 2002 05:08:07 +0200
From: Andi Kleen <ak@suse.de>
To: John Levon <levon@movementarian.org>
Cc: linux-kernel@vger.kernel.org, ak@suse.de
Subject: Re: [PATCH][RFC] oprofile for 2.5.39
Message-ID: <20020929050807.A17869@wotan.suse.de>
References: <20020929014440.GA66796@compsoc.man.ac.uk.suse.lists.linux.kernel> <p737kh5sf45.fsf@oldwotan.suse.de> <20020929025224.GA68153@compsoc.man.ac.uk>
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> 
> Basically it's a matter of :
> 
> 	task_struct *
> 	EIP/Event
> 	EIP/Event
> 	EIP/Event
> 	EIP/Event
> 	....

I think you can easily do that by keeping state per cpu in the 
NMI handler.

	if (current == __get_cpu_var(oprofile_cpustate)) { 
		/* log current */
		__get_cpu_var(oprofile_cpustate) = current; 	
	} else { 
		/* do nothing */ 
	}
	/* log EIP */

[or when you are an module use an cache line padded array indexed with
smp_processor_id - per cpu data doesn't work from modules]

This is even more efficient because when the NMI rate is lower than
the task switch frequency (which is not unlikely) then you'll avoid
many useless task_struct loggings.

-Andi