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Date:	Thu, 2 Dec 2010 11:15:02 -0500
From:	Don Zickus <>
To:	Peter Zijlstra <>
Cc:	"Eric W. Biederman" <>,
	Vivek Goyal <>,
	Yinghai Lu <>, Ingo Molnar <>,
	Jason Wessel <>,
	"" <>,
	Haren Myneni <>
Subject: Re: perf hw  in kexeced kernel broken in tip

On Thu, Dec 02, 2010 at 08:34:30AM +0100, Peter Zijlstra wrote:
> On Thu, 2010-12-02 at 00:23 -0500, Don Zickus wrote:
> > On Wed, Dec 01, 2010 at 01:48:07PM -0800, Eric W. Biederman wrote:
> > > >
> > > > Oh, but I'm not a device or sysdev thing, I'll never get something like
> > > > that.
> > > 
> > > There is also the reboot notifier, if the NMI needs to be controlled
> > > outside of device model.  Sigh. The NMI handling is such a special case.
> > 
> > I tried reboot notifiers with the nmi_watchdog and acheived some success
> > (on a Westmere box, a P4 still failed).  Kdump is still screwed, but maybe
> > we don't care for now.
> > 
> > Here is the quick and dirty patch I used.
> We'd really want a perf_event.c callback there to do as the hot-unplug
> code does and detach all running counters from the cpu.

Ok, I moved the reboot notifier stuff from kernel/watchdog.c to
kernel/perf_event.c.  Things still worked fine from a kexec perspective.

Vivek suggested to me this morning that I should just blantantly disable the
perf counter during init when running my test.  Looking through the code I
don't think I can do this using disable_all because some routines look for
the active bit to be set and some arches have different disable registers
than others.  Thoughts?

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