Date: Thu, 7 Jun 2007 21:18:16 +0300 From: "Abdullah Ibn Hamad Al-Marri" <almarrie@gmail.com> To: "Chuck Swiger" <cswiger@mac.com> Cc: freebsd-current@freebsd.org, Andrew Thompson <thompsa@freebsd.org> Subject: Re: Why not remove polling(4) from 7.0? Message-ID: <499c70c0706071118l6410dc5dqce32b86fd919de3@mail.gmail.com> In-Reply-To: <29EFA5CA-6232-45AA-A10D-0A45BB3E2100@mac.com> References: <499c70c0706070210v39f7016hbd80e9780902e992@mail.gmail.com> <20070607093027.GA4784@heff.fud.org.nz> <499c70c0706070236x28d781e6yb8ba4c8ccd251372@mail.gmail.com> <29EFA5CA-6232-45AA-A10D-0A45BB3E2100@mac.com>
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On 6/7/07, Chuck Swiger <cswiger@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? -- Regards, -Abdullah Ibn Hamad Al-Marri Arab Portal http://www.WeArab.Net/
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