Messages in this thread | | | Date | Thu, 22 Jun 2006 05:47:00 -0700 (PDT) | From | Danial Thom <> | Subject | Re: Dropping Packets in 2.6.17 |
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--- Arjan van de Ven <arjan@infradead.org> wrote:
> On Thu, 2006-06-22 at 04:31 -0700, Danial Thom > wrote: > > I'm trying to make a case for using linux as > a > > network appliance, but I can't find any > > combination of settings that will keep it > from > > dropping packets at an unacceptably high > rate. > > The test system is a 1.8Ghz Opteron with > intel > > gigE cards running 2.6.17. I'm passing about > 70K > > pps through the box, which is a light load, > but > > userland activities (such as building a > kernel) > > cause it to lose packets, even with backlog > set > > to 20000. I had the same problem with 2.6.12 > and > > abandoned the effort. Has anything been done > > since to give priority to networking? You > can't > > have a network appliance drop packets when > some > > application is gathering stats or a user is > > looking at a graph. What tunings are > available? > > Hi Danial, > > the most likely tunable that will help you is > > /proc/sys/vm/min_free_kbytes > > For the router kind of device that one usually > needs bumping a bit; > without the bumping the VM doesn't see enough > "normal" activity to tune > it's emergency/interrupt handling buffers (and > most networking > allocations happen in interrupt context), and > then ends up failing > allocations in interrupt context, which leads > to dropped packets.
I don't think thats the problem, as I've tracked the problem to packets being dropped because of excessive backlog (ie, they are being dropped gracefully). However with a backlog of 20000, and a traffic level of about 75,000pps, that means almost 1/3 of a second that the system doesn't process packets, which is just unacceptable.
I'll try changing the setting, but running out of memory doesn't seem to be the issue. I think what I need is some mechanism to make interrupts a priority, like it was back in the days when networking was more important then mp3 playback.
Danial
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