linux-kernel - Re: Drop WARN on AMD lack of perfctrs

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Date:	Fri, 17 May 2013 00:33:45 +0200
From:	Robert Richter <rric@...nel.org>
To:	Josh Boyer <jwboyer@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	x86@...nel.org, linux-kernel@...r.kernel.org, gleb@...hat.com
Subject: Re: Drop WARN on AMD lack of perfctrs

On 16.05.13 17:54:59, Josh Boyer wrote:
> On Thu, May 16, 2013 at 10:55:58PM +0200, Robert Richter wrote:
> > On 16.05.13 20:10:18, Peter Zijlstra wrote:
> > > I would make it a FW_BUG as well. But yeah, I suppose that is a better option
> > > than the WARN_ON. Unless Robert had a different reason...
> > 
> > iirc the reason was the different msr range that is switched on fam15h
> > with a different counter to counter msr offset of 2 instead of 1. The
> > code relies on the assumption that the msrs exist on that cpu. Thus
> > the warning if not. Also note that code may have changed in 3.10 in
> > that area.
> 
> Again, what is someone supposed to do with a backtrace from the WARN?
> As far as I can see, a user can't really do anything other than report
> it and then there's nothing to fix.
> 
> The code might have moved in 3.10, but the WARN is still there.
> 
> Would you like me to send a patch to get it reduced to pr_err?

I wrote the code with the assumption of a certain system layout which
was the check for. Now, in a vm this assumption is no longer valid.
Will change the code in a way this is handled properly.

-Robert
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