Messages in this thread |  | | | Date | Wed, 1 Dec 2010 14:58:35 -0500 | | From | Vivek Goyal <> | | Subject | Re: perf hw in kexeced kernel broken in tip |
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On Wed, Dec 01, 2010 at 08:49:49PM +0100, Peter Zijlstra wrote: > 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.
I think we already call ->shutdown() in regular reboot path.
kernel_restart() kernel_restart_prepare() device_shutdown(); sysdev_shutdown();
So it should not make lot of difference if perf subsystem/counters are also shutdown using ->shutdown().
> > > 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.
I would not know the history but I have heard stories that if you don't shutdown the hardware over restart, BIOS might not be expecting it and might get trumped.
Thanks Vivek
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