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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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