Messages in this thread | | | From | (Eric W. Biederman) | Date | Wed, 01 Dec 2010 13:48:07 -0800 | Subject | Re: perf hw in kexeced kernel broken in tip |
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Peter Zijlstra <peterz@infradead.org> writes:
> On Wed, 2010-12-01 at 14:58 -0500, Vivek Goyal wrote: >> 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(). > > 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.
>> > > 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. > > Never yet had a problem with that.
I haven't personally but I have certainly heard stories and seen debugging sessions where some devices work or don't depending on the order of running linux and windows on a machine, with soft reboots in between.
Eric
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