Re: NO_HZ: timer interrupt stuck [Re: Linux 2.6.21-rc1]

From: Thomas Gleixner
Date: Wed Feb 21 2007 - 18:12:49 EST


On Thu, 2007-02-22 at 00:04 +0100, Luca Tettamanti wrote:
> Hi Thomas,
> I'm testing NO_HZ on my machines. On the laptop I see that the timer
> interrupt counter is incremented (though slower than HZ). This machine
> is running UP kernel.
>
> On my desktop I see this:
>
> CPU0 CPU1
> 0: 114 0 IO-APIC-edge timer
> 1: 1624 10771 IO-APIC-edge i8042
> 6: 3 0 IO-APIC-edge floppy
> 7: 0 0 IO-APIC-edge parport0
> 9: 0 0 IO-APIC-fasteoi acpi
> 12: 40111 184047 IO-APIC-edge i8042
> 16: 75624 998858 IO-APIC-fasteoi radeon@pci:0000:01:00.0, uhci_hcd:usb1
> 17: 0 0 IO-APIC-fasteoi uhci_hcd:usb4
> 18: 711 5487 IO-APIC-fasteoi ide1, libata, ehci_hcd:usb7, uhci_hcd:usb3
> 19: 617 2254 IO-APIC-fasteoi libata, uhci_hcd:usb2
> 20: 0 0 IO-APIC-fasteoi ehci_hcd:usb6, uhci_hcd:usb5
> 21: 2483869 0 IO-APIC-fasteoi eth0
> 22: 2 0 IO-APIC-fasteoi ohci1394
> 218: 28872 360643 PCI-MSI-edge HDA Intel
> 219: 32932 138196 PCI-MSI-edge libata
> NMI: 0 0
> LOC: 2761191 2827539
> ERR: 0
> MIS: 0
>
> Interrupt 0 is stuck at 114 (the number is consistent across reboots). I
> don't experience any problem, time is running fine. Still it's strange
> that the timer is doing nothing; maybe something other than the PIT is
> used for time keeping?

Yes, we switch away from PIT and use the local APIC timer. (LOC)

tglx


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