On Tuesday 26 June 2007, JD Bronson wrote:
> Anyone using device polling on 6.2stable (i386) ?
I have been using it.
> I have been reading up on this and seen some good and some bad but
> nothing definitive.
Basically you improve efficiency at the cost of latency, so expect lower CPU
usage. To reduce latency one can increase HZ.
>
> I have bge NICs in these machines and they are running as routers,
> and running pf.
>
> When I enabled it in the kernel and then via rc.conf (since sysctl
> use is depreciated now) ...I can see a difference in "vmstat -i"
> presuming thats the correct way to check.
Yes that would work.
>
> With polling DISABLED...vmstat shows ever increasing values for example:
>
> vmstat -i
> interrupt total rate
> irq4: sio0 3 0
> irq6: fdc010 0
> irq14: ata012210 0
> irq15: ata178834 2
> irq22: bge0 430416 11
> irq23: bge1 917826 24
> cpu0: timer 75098549 2000
> cpu1: timer 75092636 1999
> Total 151630484 4038
>
> and when I do a large network operation (like ftp an ISO) it
> increases and increaseshowever, with device polling compiled and
> configured (all default values though in sysctl) - I do not see an
> increase in vmstat numbers for the nics...I figured thats good...but
> I might be wrong?
Yup that's good. With polling off, you should never see it increase much
beyond ~8000 interrupts/sec, the theoretical limit for an 100mbit connection
with 1500 mtu while doing a big transfer. You can also check with
systat -vmstat 1.
>
> I dont do anything higher than WAN(10MB) and LAN(100MB).
>
> But if anyone has any suggestions or comments -especially values to
> adjust in sysctl, please chime in.
If you want lower latency (or if you experience packet loss) you could set
the kern.hz tunable (in loader.conf) to something higher than the default
1000. I believe that people have been using 1 for busy routers. Note that
this will increase CPU load when the system has no packets to process.
>
> TIA
>
> -JD
Cheers,
Pieter de GOeje
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