Re: perf hw in kexeced kernel broken in tip

Peter Zijlstra
2010-12-01T19:49:36Z

On Wed, 2010-12-01 at 14:46 -0500, Vivek Goyal wrote:
> On Wed, Dec 01, 2010 at 08:38:12PM +0100, Peter Zijlstra wrote:
> > On Wed, 2010-12-01 at 11:23 -0500, Vivek Goyal wrote:
> > > > What does kexec normally do to ensure hardware is left in a sane state?
> > >
> > > Typically calls device_shutdown() and sysdev_shutdown() from
> > > kernel_restart_prepare() to shutdown the devices.
> > >
> > > Also calls machine_shutdown() which depending on architecture can take
> > > care of various things like stopping other cpus, shutting down LAPIC,
> > > disabling IOAPIC, disabling hpet, shutting down IOMMU etc
> > > (native_machine_shutdown()).
> >
> > So basically there's no sane generic reset callout?
>
> I think ->shutdown() calls are sane generic callouts. Isn't it?

->shutdown looks like it's about to reset/halt the hardware, no point in
slowing down the regular shutdown/reboot path for something like this,
we know the hardware will get reset to a sane state.

> There seem to be few exceptions for LAPIC, IOMMU and HPET and I am not
> sure why they are not covered by shutdown calls. CCing Eric, he might
> have more insight into it.

That's all arch specific, but even there I don't think the reset code
should live outside of kexec.