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Date: Wed, 8 Dec 2010 09:39:22 -0500
From: Vivek Goyal <vgoyal@redhat.com>
To: Don Zickus <dzickus@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Yinghai Lu <yinghai@kernel.org>, 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
Message-ID: <20101208143922.GA31703@redhat.com>
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 <20101202052321.GH18100@redhat.com>
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On Wed, Dec 08, 2010 at 09:01:03AM -0500, Don Zickus wrote:
> On Wed, Dec 08, 2010 at 12:30:20AM +0100, Peter Zijlstra wrote:
> > On Thu, 2010-12-02 at 11:15 -0500, Don Zickus wrote:
> > 
> > > Vivek suggested to me this morning that I should just blantantly disable the
> > > perf counter during init when running my test. 
> > 
> > Nah, we should actively scan for that during the bring-up and kill
> > hw-perf when we find an enable bit set, some BIOSes actively use the
> > PMU, this is something that should be discouraged.
> 
> Ok, the reboot notifier addresses the kexec problem but doesn't fix it
> though (I have to test to confirm that, comments below).  The bios check
> should catch those situations (ironically I stumbled upon a machine with
> this problem, so I will test your patch with it, though it only uses perf
> counter 0).  The kdump problem will still exist, not sure if we care and
> perhaps we should document in the changelog that we know kdump is still
> broken (unless we do care).

Can't think why would somebody like to use performance counters in kdump
kernel. So that probably should not be a concern.

Vivek