Re: nmi_watchdog=2 regression in 2.6.21

Daniel Walker
2007-08-31T16:45:26Z

On Fri, 2007-08-31 at 09:21 -0700, Stephane Eranian wrote:
> Daniel,
>
> On Fri, Aug 31, 2007 at 07:43:20AM -0700, Daniel Walker wrote:
> > On Thu, 2007-08-30 at 14:05 -0700, Stephane Eranian wrote:
> > > Daniel,
> >
> > > Yes, I realized I missed a small detail in the switch statement.
> > > Could you try the new version?
> >
> > This patch still has the stuck NMI .. Essentially the same thing that
> > happened without the patch..
> >
> Ok, looks like deaulting to P6 does not quite work.
>
> Here is a new version. This time I used a different approach.
> I am must admit I am a bit puzzled by the duplication of information
> between the wd_ops and the nmi_watchdog_ctlblk structure. My understanding
> is that thelater is used as a cache for the info that needs to be per-cpu.
>
> The wd_ops provides the MSR to use for the counter, yet all the setup_*()
> routines hardcode the MSR. Not sure why?

Yeah, that's bad .. For instance, if those had all been centralized
Bjorn wouldn't have needed to fix those up later..

> In this patch, the setup_*() routine now extract the MSR from the wd_ops
> to copy them into the nmi_watchdog_ctlblk. This is not done for P4 because
> of the special and ugly case of HT.
>
> With this approach, we can now create a custom wd_ops for CoreDuo that is
> a clone of the intel_arch_wd_ops, except for the MSR.
>
> Could you try this one instead?

So I tested your patch unchanged and the system boots, and the
check_nmi_watchdog() passes .. However, the nmi stops ticking right
after bootup,

>From my /proc/interrupts below,

CPU0 CPU1 CPU2 CPU3
0: 108 0 0 0 IO-APIC-edge timer
1: 0 0 0 8 IO-APIC-edge i8042
4: 3427 0 0 1 IO-APIC-edge serial
8: 1 0 0 1 IO-APIC-edge rtc
12: 0 0 0 113 IO-APIC-edge i8042
14: 1128 0 0 10 IO-APIC-edge ide0
16: 1664 0 0 1 IO-APIC-fasteoi uhci_hcd:usb2, eth0
18: 0 0 0 0 IO-APIC-fasteoi ehci_hcd:usb1
19: 0 0 0 0 IO-APIC-fasteoi uhci_hcd:usb3
20: 0 0 0 1 IO-APIC-fasteoi acpi
NMI: 1670 1453 1097 967
LOC: 48001 48002 48000 48006
ERR: 0
MIS: 0

The NMI field never changes ..

So I added another change which looked appropriate,

@@ -674,6 +688,7 @@ unsigned lapic_adjust_nmi_hz(unsigned hz
{
struct nmi_watchdog_ctlblk *wd = &__get_cpu_var(nmi_watchdog_ctlblk);
if (wd->perfctr_msr == MSR_P6_PERFCTR0 ||
+ wd->perfctr_msr == MSR_ARCH_PERFMON_PERFCTR0 ||
wd->perfctr_msr == MSR_ARCH_PERFMON_PERFCTR1)
hz = adjust_for_32bit_ctr(hz);
return hz;

Unfortunately that didn't fix anything, but I have a feeling is has
something to do with the nmi hertz adjustment that happens after
check_nmi_watchdog() ..

Daniel