Why is em nic generating interrupts?
Don Bowman
don at sandvine.com
Thu Oct 9 08:04:25 PDT 2003
From: Terry Lambert [mailto:tlambert2 at mindspring.com]
> "Michael O. Boev" wrote:
> > I've got a [uniprocessor 5.1-RELEASE] router machine with
> fxp and em nics.
> > I've built my kernel with the following included:
> >
> > options DEVICE_POLLING
> > options HZ=2500
> >
> > and enabled polling in /etc/sysctl.conf.
> [ ... ]
> > What's happening? Is polling working in my case?
> > If yes, why is vmstat showing interrupts? I see clearly,
> > that fxp's counter doesn't increase, and em's is constantly growing.
> >
> > Is there anyone who knows for sure that em's polling works?
>
> You may want to ask Luigi; polling is his code.
>
> However, I believe the issue is that polling doesn't start
> until you take an interrupt, and it stops as soon as there is
> no more data to process, and waits for the next interrupt.
>
> If you were to jack your load way up, you would probably see
> an increase in interrupts, then them dropping off dramatically.
>
> If all else fails, read the source code... 8-).
FWIW, this works for me with 4.7. As terry says, you
do see a couple of initial interrupts, as below, and
then they stop.
$ vmstat -i
interrupt total rate
em0 irq16 4 0
em1 irq17 4 0
ahc0 irq18 5653 0
ahc1 irq19 15 0
em2 irq20 4 0
mux irq21 3 0
sio0 irq4 1583 0
sio1 irq3 1 0
clk irq0 14545633 2501
rtc irq8 744224 128
Total 15297124 2631
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