Re: perf hw in kexeced kernel broken in tip

Vivek Goyal
2010-12-08T14:39:51Z

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