Timer interrupt lost on some x86_64 systems

Neil Horman nhorman at redhat.com
Mon Nov 12 10:17:21 EST 2007

On Mon, Nov 12, 2007 at 10:19:03AM +0530, Vivek Goyal wrote:
> On Wed, Nov 07, 2007 at 09:00:06AM -0500, Neil Horman wrote:
> > Hey all-
> > 	I've been getting reports of some x86_64 systems that, on kdump kernel
> > boot get stuck in calibrate_delay(),  in both RHEL kernels and upstream kernels.
> > The current thinking is that the lapic timer interrupt is no longer getting
> > delivered, likely because we handle a crash condition on a cpu that isn't the
> > boot cpu.  One known offender is this motherboard:
> > http://www.supermicro.com/Aplus/motherboard/Opteron8000/MCP55/H8QM8-2.cfm
> > My current thought is that the TIMER_LVT entry is masked on all but the boot cpu
> > on this system (which is strange, as I was under the impression that the timer
> > interrupt was supposed to be enabled on all CPU's nominally.
> I also thought that LAPIC timer interrupts are enabled on all cpus.
That doesn't appear to be the case.  The configuration I've seen is that only
one lapic has timer interrupts enabled, and the interrupt handler for the timer
interrupt broadcasts the interrupt to all the other processors via IPI

> >  At any rate, I was
> > going to try to read/write the TIMER_LVT on the crashing processor before we
> > jump to purgatory, or in purgatory itself, to see if that fixes the problem, but
> I think calibrate_dealy() depends on external timer interrupt coming and
> not the local APIC timer interrupt. Generally it is 8254 timer chip. Now a
> days motherboards seems to be having HPET and I know somebody has reported
> problems with HPET where HPET interrupts are not coming in second kernel and
> system hangs in second kernel. I suspect  that same might be the issue here.
Perhaps, do you have a pointer to any list discussions on the subject?  I've not
seen any yet.


> Thanks
> Vivek

 *Neil Horman
 *Software Engineer
 *Red Hat, Inc.
 *nhorman at redhat.com
 *gpg keyid: 1024D / 0x92A74FA1

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