linux-kernel - Re: [PATCH 0/2] oprofile: introduce module parameter oprofile.cpu

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Date:	Wed, 6 May 2009 18:39:57 +0200
From:	Robert Richter <robert.richter@....com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	oprofile-list <oprofile-list@...ts.sourceforge.net>
Subject: Re: [PATCH 0/2] oprofile: introduce module parameter
	oprofile.cpu_type

On 06.05.09 16:47:20, Andi Kleen wrote:
> On Wed, May 06, 2009 at 02:39:12PM +0200, Robert Richter wrote:
> > The current userland does not yet fully support all cpu types
> > implemented in the kernel. With the module parameter oprofile.cpu_type
> > a certain cpu type can be reported to the oprofile userland and thus
> > makes the kernel usable with current distros.
> 
> On Intel systems forcing archperfmon is the only one that makes sense
> nd only if the CPU supports arch perfmon(btw that's already in my patchkit
> which you haven't commented on so far)
> 
> I don't thinking forcing core2 on a system like Nehalem with completely
> different events is a good idea though. This just means if the user
> selects anything unusual they will get junk data, which is just
> a bad design.

It is a kernel parameter, and users should know what they are doing
and what the risks are. I assume counting cpu clk unhalted will work
and some other events too. So the patch does not hurt.

> Also if you force core2 on a P4 system the kernel will just oops
> because it will access MSRs that are not there. So I don't think
> that's a good idea.

It anables core_2 only on family 6 (ppro implementation).

> 
> It means you have to update oprofile userland at least once until
> you have arch perfmon support, but I think even Linus will be able
> to do that :) Hopefully Maynard will do a new release soon.

I agree, a new release of the userland would be the best. But till
then it is at least 1-2 months to go.

> The force of core2 is nacked from my side.

I do not have any passion with this patch, What I have in mind is
"oprofile sucks", and this patch would make oprofile more usable.

-Robert

-- 
Advanced Micro Devices, Inc.
Operating System Research Center
email: robert.richter@....com

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