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

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Message-ID: <20101208143922.GA31703@redhat.com>
Date:	Wed, 8 Dec 2010 09:39:22 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Don Zickus <dzickus@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Yinghai Lu <yinghai@...nel.org>, 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, 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
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