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

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Date:	Wed, 08 Dec 2010 11:20:59 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Peter Zijlstra <peterz@...radead.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 12/08/2010 11:17 AM, Peter Zijlstra wrote:
> 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.

ok, thanks.
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