linux-kernel - Re: [RFC] new MSR r/w functions per CPU

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Date:	Wed, 13 Dec 2006 17:10:26 -0500
From:	Dave Jones <davej@...hat.com>
To:	Rudolf Marek <r.marek@...embler.cz>
Cc:	hpa@...or.com, norsk5@...ssion.com,
	lkml <linux-kernel@...r.kernel.org>,
	LM Sensors <lm-sensors@...sensors.org>,
	bluesmoke-devel@...ts.sourceforge.net
Subject: Re: [RFC] new MSR r/w functions per CPU

On Wed, Dec 13, 2006 at 10:45:13PM +0100, Rudolf Marek wrote:
 > Hello all,
 > 
 > For my new coretemp driver[1], I need to execute the rdmsr on particular 
 > processor.  There is no such "global" function for that in the kernel so far.
 > 
 > The per CPU msr_read and msr_write are used in following drivers:
 > 
 > msr.c (it is static there now)
 > k8-edac.c  (duplicated right now -> driver in -mm)
 > coretemp.c (my new Core temperature sensor -> driver [1])
 > 
 > Question is how make an access to that functions. Enclosed patch does simple 
 > EXPORT_SYMBOL_GPL for them, but then both drivers (k8-edac.c and coretemp.c) 
 > would depend on the MSR driver. The ultimate solution would be to move this type
 > of function to separate module, but perhaps this is just bit overkill?

Exposing the guts of the msr driver like that doesn't seem too clean.
For in-kernel use, why not just add something like this..
(note:not even compile tested)..

void rdmsr_on_cpu(unsigned int cpu, unsigned long msr, unsigned long *lo, unsigned long *hi)
{
    cpumask_t oldmask;

    oldmask = current->cpus_allowed;
    set_cpus_allowed(current, cpumask_of_cpu(cpu));

	rdmsr(msr, &lo, &hi);

    set_cpus_allowed(current, oldmask);
}


		Dave

-- 
http://www.codemonkey.org.uk
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