[PLUG] What is softirq?

Jason R. Martin nsxfreddy at gmail.com
Wed Sep 21 12:07:50 PDT 2005


On 9/21/05, Vincent Yau <v_yau3 at hotmail.com> wrote:
> Hi:
>
> Recently, I brought up to athlon64 box.  They both run great (most of the
> time).
> The slower of the two, however, seems to be exhibiting some weird
> behavior at times.  They are all sorts of them here and there
> and I am slowly tackling one at a time.
>
> This one, however, is a little odd for me.
> When I run top,   I can always see that under "CPU states", the "softirq"
> category always
> hovers around 50% usage.  Even when I am not running anything (other than
> what is minimum to have the box running), it would be 50% idle and 50%
> softirq.
> I don't see this on any other boxes so I am wondering what is special about
> this.
> Can someone tell me what is softirq?
>
> I am running kernel 2.4.21-32.EL  64-bit version
>
> Thanks for any tip/pointer.

softirqs are software interrupts, used often by device drivers to do
further processing of something outside of the hardware interrupt
handler, which needs to run as fast as possible so interrupts can be
re-enabled.  Perhaps you have some rogue hardware?  Does
/proc/interrupts show something going crazy?  Is the box receiving a
lot of network traffic?  Anything in your logs?

I found this guy's posting, perhaps you should try the "noapic" option
to see if that fixes it, then file a bug with RedHat.

http://kerneltrap.org/node/5534

Jason



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