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    SubjectRe: [Bug #12650] Strange load average and ksoftirqd behavior with 2.6.29-rc2-git1

    * Damien Wyart <damien.wyart@free.fr> wrote:

    > > Also, could you send the output of:
    >
    > > http://people.redhat.com/mingo/cfs-scheduler/tools/cfs-debug-info.sh
    >
    > > Run it while you can see the ksoftirqd anomaly.
    >
    > In fact I see it all the time when the machine is idle. When something
    > runs (spamd for example), the running time of ksoftirqd stops
    > increasing, and it goes back to increasing like crazy when idle state
    > comes back.

    here's the ksoftirqd stats from your data:

    top - 08:09:20 up 2 min, 1 user, load average: 0.95, 0.35, 0.13
    Tasks: 100 total, 1 running, 99 sleeping, 0 stopped, 0 zombie
    Cpu(s): 0.4%us, 1.3%sy, 0.0%ni, 89.2%id, 0.0%wa, 0.0%hi, 9.0%si, 0.0%st
    Mem: 2074980k total, 236544k used, 1838436k free, 5032k buffers
    Swap: 1212896k total, 0k used, 1212896k free, 66016k cached

    PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
    2280 root 15 -5 0 0 0 S 22 0.0 0:06.39 [ksoftirqd/1]
    2452 root 20 0 2400 1132 888 R 1 0.1 0:00.02 top -H -c -b -d 1 -
    1 root 20 0 2100 688 588 S 0 0.0 0:00.48 init [2]
    2 root 15 -5 0 0 0 S 0 0.0 0:00.00 [kthreadd]

    ksoftirqd really seems to be active (according to scheduler stats), and
    has gathered more than 6 seconds of runtime after 2 minutes of uptime -
    that is clearly anomalous.

    The main method how softirqs get generated are hardirqs, but the hardirq
    is low on your box (as expected):

    -- interrupts: --
    CPU0 CPU1
    0: 155 0 IO-APIC-edge timer
    1: 2 0 IO-APIC-edge i8042
    7: 0 0 IO-APIC-edge parport0
    8: 2 0 IO-APIC-edge rtc
    9: 0 0 IO-APIC-fasteoi acpi
    12: 4 0 IO-APIC-edge i8042
    14: 0 0 IO-APIC-edge ata_piix
    15: 132 0 IO-APIC-edge ata_piix
    16: 213 0 IO-APIC-fasteoi uhci_hcd:usb2, uhci_hcd:usb5
    18: 6908 0 IO-APIC-fasteoi ata_piix, uhci_hcd:usb4
    19: 221 0 IO-APIC-fasteoi uhci_hcd:usb3
    20: 1072 0 IO-APIC-fasteoi eth0
    21: 0 0 IO-APIC-fasteoi EMU10K1
    23: 4 0 IO-APIC-fasteoi ehci_hcd:usb1
    NMI: 0 0 Non-maskable interrupts
    LOC: 79306 74184 Local timer interrupts
    CNT: 0 0 Performance counter interrupts
    RES: 32672 13541 Rescheduling interrupts
    CAL: 8 40 Function call interrupts
    TLB: 235 591 TLB shootdowns
    TRM: 0 0 Thermal event interrupts
    SPU: 0 0 Spurious interrupts
    ERR: 0
    MIS: 0

    about 200K irqs - most of which are lapic timer irqs. Thus 6 seconds of
    ksoftirqd runtime is way too much.

    Ingo


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