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

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Message-ID: <1291835855.28378.149.camel@laptop>
Date:	Wed, 08 Dec 2010 20:17:35 +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 11:05 -0800, Yinghai Lu wrote:
> On 12/08/2010 11:01 AM, Don Zickus wrote:
> > On Wed, Dec 08, 2010 at 10:43:14AM -0800, Yinghai Lu wrote:
> >>
> >> can you add sth force_... in command line to take over ownership of perf from BIOS or previous kernel ?
> >>
> >> then still can use perf etc after we kexec from RHEL or SLES kernel to later kernel ( from 2.6.37)
> > 
> > My understand is that you can't because the BIOS is actively using it
> > behind the scenes of the kernel (well during an SMI).  I have a machine
> > where I tried to force take it but it still stopped triggering interrupts.
> 
> how about second case: kexec from RHEL 6 stock kernel to upstream kernel ?

Its impossible to distinguish between a BIOS having claimed a counter
and a previous kernel not having shut things down properly.

The best we can do is allow a force parameter and let the user keep all
pieces when he uses it.
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