linux-kernel - Re: [2.6.33-rc1] System timer flooding bus on Lenovo Thinkpad W500 laptop in x86

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Message-ID: <4B301744.2010404@gmail.com>
Date:	Mon, 21 Dec 2009 18:48:04 -0600
From:	Robert Hancock <hancockrwd@...il.com>
To:	Shawn Starr <shawn.starr@...ers.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [2.6.33-rc1] System timer flooding bus on Lenovo Thinkpad W500
 laptop in x86_64

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
> enabled.
>
> 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)
> x86_64
>    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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