linux-kernel - Re: perf hw in kexeced kernel broken in tip

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Message-ID: <1291232989.32004.1987.camel@laptop>
Date:	Wed, 01 Dec 2010 20:49:49 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Yinghai Lu <yinghai@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	Jason Wessel <jason.wessel@...driver.com>,
	Don Zickus <dzickus@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Haren Myneni <hbabu@...ibm.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: perf hw  in kexeced kernel broken in tip

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.
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