Re: [2.6.33-rc1] System timer flooding bus on Lenovo Thinkpad W500laptop in x86_64

From: Robert Hancock
Date: Mon Dec 21 2009 - 19:48:15 EST

On 12/21/2009 12:12 PM, Shawn Starr wrote:
Hello kernel devs,

I am noticing a serious problem with the system timer flooding the bus with
many interrupts for no reason. I have compiled the kernel with tickless

Can someone provide me some debugging to find out why this is happening?

As a comparsion my quad core box has no such issue: (Running 2.6.32-rc7)
0: 42 4 1 1 IO-APIC-edge timer

That's not really a fair comparison, that box is likely using the APIC timer (which will be on a different line) instead of the PC timer. Those 48 interrupts likely all occurred just after boot.

my Lenovo ThinkPad W500 (latest BIOS 3.11) laptop shows the system timer
flooding the bus (Running 2.6.33-rc1) x86_64
0: 66775 70429 IO-APIC-edge timer<-- keeps rising, rapidly

and afew minutes ...

0: 119849 124505 IO-APIC-edge timer

Same for Rescheduling interrupts rising just as fast with the timer.

This does not look right, powertop shows:

40.0% ( 62.1)<kernel IPI> : Rescheduling interrupts
22.9% ( 35.6)<interrupt> : extra timer interrupt
17.0% ( 26.4)<interrupt> : iwlagn

and another sample...

54.6% (144.8)<kernel IPI> : Rescheduling interrupts
14.6% ( 38.8)<interrupt> : extra timer interrupt
8.5% ( 22.6)<interrupt> : iwlagn
6.5% ( 17.2)<interrupt> : uhci_hcd:usb6, radeon@pci:0000:01:00.0
6.5% ( 17.2) USB device 6-1 : Microsoft Basic Optical Mouse v2.0
(Microsoft )

There is no cause for the rescheduling interrupts and extra timer interrupt to
wakeup the CPUs so much? Are there any timer issues?

Can you post full dmesg and /proc/interrupts output?
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