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Date: Wed, 08 Dec 2010 11:20:59 -0800
From: Yinghai Lu <yinghai@kernel.org>
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To: Peter Zijlstra <peterz@infradead.org>
CC: Don Zickus <dzickus@redhat.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Vivek Goyal <vgoyal@redhat.com>, Ingo Molnar <mingo@elte.hu>,
        Jason Wessel <jason.wessel@windriver.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Haren Myneni <hbabu@us.ibm.com>
Subject: Re: perf hw  in kexeced kernel broken in tip
References: <1291234036.32004.2008.camel@laptop>	 <m162vdp3l4.fsf@fess.ebiederm.org> <20101202052321.GH18100@redhat.com>	 <1291275270.4023.20.camel@twins> <20101202161502.GL18100@redhat.com>	 <1291764620.2032.1293.camel@laptop> <20101208140103.GM21786@redhat.com>	 <1291818005.28378.38.camel@laptop> <1291820356.28378.83.camel@laptop>	 <4CFFD1C2.1080108@kernel.org> <20101208190158.GA8565@redhat.com>	 <4CFFD715.4090900@kernel.org> <1291835855.28378.149.camel@laptop>
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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.