Why not remove polling(4) from 7.0?

Abdullah Ibn Hamad Al-Marri almarrie at gmail.com
Thu Jun 7 18:18:18 UTC 2007

On 6/7/07, Chuck Swiger <cswiger at mac.com> wrote:
> On Jun 7, 2007, at 2:36 AM, Abdullah Ibn Hamad Al-Marri wrote:
> >> > So why not remove it or switch to adaptive polling as em(4)
> >> instead of
> >> > resorting to polling?
> >>
> >> Are you just talking about em(4) or removing polling for all
> >> drivers? It
> >> is helpful in some cases, for example I run FreeBSD on a Nortel
> >> contivity 1010 box where interrupts do not work on the fxp
> >> interface and
> >> yet its quite usable with polling mode.
> >>
> >> Its not enabled by default so its up to the user if they want to make
> >> use of it.
> >
> > I mean can't we use better handeling for nics which is better than
> > current polling(4)?
> If a particular NIC supports something like interrupt mitigation,
> generally it will be enabled by default.  Of course, using interrupt
> mitigation adds latency also, just as using polling does, but the
> tradeoffs are probably worth it for many cases.
> However, under other circumstances-- such as continuous or nearly
> continuous high traffic loads on something like a router or firewall
> application-- polling tends to handle such load better and avoid
> livelock and/or excessive context switches to the interrupt handler
> resulting in lower throughput.  The key point to notice is that
> polling is not the default behavior, it's an option which can be
> selectively enabled when the admin of a particular machine decides
> that it might prove to be the better choice.
> And, as Andrew mentioned, in a few cases you'll find a machine where
> the NIC doesn't fire interrupts off correctly at all, generally due
> to some major flaw in the hardware or BIOS config, but polling will
> still work OK.
> --
> -Chuck

So it's recommended to use polling if I run pf and deals with DDoS?


-Abdullah Ibn Hamad Al-Marri
Arab Portal

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