linux-kernel - Re: [PATCH] x86, kdump: No need to disable ioapic in crash path

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Message-ID: <20120207221924.GH6346@redhat.com>
Date:	Tue, 7 Feb 2012 17:19:24 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Don Zickus <dzickus@...hat.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>, x86@...nel.org,
	LKML <linux-kernel@...r.kernel.org>,
	kexec-list <kexec@...ts.infradead.org>
Subject: Re: [PATCH] x86, kdump: No need to disable ioapic in crash path

On Tue, Feb 07, 2012 at 04:57:41PM -0500, Don Zickus wrote:
> On Thu, Feb 02, 2012 at 03:24:46PM -0800, Eric W. Biederman wrote:
> > > Eric, brought up a point that because the boot code was restructured we may
> > > not need to disable the io apic any more in the crash path.  The original
> > > concern that led to the development of disable_IO_APIC, was that the TSC
> > > calibration on boot up relied on the PIT timer for reference.  Access
> > > to the PIT required 8259 interrupts to be working.  This wouldn't work
> > > if the ioapic needed to be configured.  So on panic path, the ioapic was
> > > reconfigured to use virtual wire mode to allow the 8259 to passthrough.
> > 
> > A small clarification originally it was the jiffies calibration that
> > would fail if we could cause the PIT to generate interrupts through the
> > 8259.  The boot would then hang at calibrating jiffies.
> 
> Ok.  Thanks!

So now what has changed? Do we setup LAPIC and IOAPIC early enough to
receive PIT interrupts in regular mode (non-virtual wire mode) or
something else?

Thanks
Vivek
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