linux-kernel - Re: perf hw in kexeced kernel broken in tip

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Date:	Wed, 08 Dec 2010 20:06:36 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Don Zickus <dzickus@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Vivek Goyal <vgoyal@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Jason Wessel <jason.wessel@...driver.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Haren Myneni <hbabu@...ibm.com>
Subject: Re: perf hw  in kexeced kernel broken in tip

On Wed, 2010-12-08 at 10:43 -0800, Yinghai Lu wrote:
> can you add sth force_... in command line to take over ownership of
> perf from BIOS or previous kernel ?

The problem is, you cannot steal the thing from the BIOS, you'll trample
on its settings and the next time it runs it will simply re-instate it.

And aside from probing the EN bit on boot there is no way of determining
this.

So forcing the state might get you an ill-functioning system.

> then still can use perf etc after we kexec from RHEL or SLES kernel to
> later kernel ( from 2.6.37)

I'm not sure why people would do that, but yeah I guess we can do
something like that.
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