Date: Tue, 12 Nov 2013 21:06:17 -0800 From: Ahmed Hamza <ahmed.hmz@gmail.com> To: Julian Elischer <julian@freebsd.org>, freebsd-ipfw@freebsd.org Subject: Re: Bursty data transfer with Dummynet Message-ID: <CAL_s3F7GhrENW4d22h01wYF%2Bf2Kd6b=BomoZ6TP5jR1HQWAQ6g@mail.gmail.com> In-Reply-To: <52830502.30809@freebsd.org> References: <CAL_s3F5Hx0XJ8Nct=urWGN72hrGQ2LT2nJfG3OxgWT5oxtjW9Q@mail.gmail.com> <52830502.30809@freebsd.org>
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On Tue, Nov 12, 2013 at 8:50 PM, Julian Elischer <julian@freebsd.org> wrote: > On 11/12/13, 6:35 PM, Ahmed Hamza wrote: >> >> Hi All, >> >> I'm trying to use Dummynet to test the behaviour of my video streaming >> application in various network conditions. Dummynet was compiled and >> installed on an Ubuntu 12.04 box with a 2.6 Linux kernel. I'm >> experiencing a strange behaviour when I reduce the bandwidth of the >> link/path. >> >> For some reason, instead of having a slow download speed. It seems as >> if the download is happening in bursts! A portion of the data is >> downloaded at a high speed, then the data transfer stops for a period >> of time and then resumes again (and so on). Does anyone have an idea >> what could be the cause? Or is this even an expected behaviour? If so, >> why? > > > I can't really speak for dummynet on Linux but the granularity of the queues > is dependent on the timer granularity of the kernel you have and to some > extent will rely on the correct integration of dummynet into the timer > facility of the kernel you are running it in. On freeBSD with a 1kHz 'tick' > I'd' expect to see packets being release from the queue each mSec or so. > if you are getting second sized chunks then it probably is a bug. Either > dummynet is not compatible with that kind of kernel, something else has gone > wrong. It COULD also be that you are catching the wrong packets.. I've seen > similar behaviour when I was accidentally queuing all the acks instead of > all the data going in the other direction, but I presume you have already > checked to see what you are queuing. > Thanks Julian and Matthew for your replies. To clarify my settings, below are the outputs from 'ipfw show' and 'ipfw pipe show'. I should also mention that it seems the by default the Ubuntu kernel is configured for 250Hz, not 1000Hz. root@vm1:~/# ipfw pipe 1 config bw 500Kbit/s queue 500Kbyte root@nsl-vm1:~/# ipfw show 00100 202247 105063701 pipe 1 ip from 192.168.56.4 to any 65535 2245577 2648958386 allow ip from any to any root@nsl-vm1:~/# ipfw pipe show 00001: 500.000 Kbit/s 0 ms 500 KB 1 queues (1 buckets) droptail mask: 0x00 0x00000000/0x0000 -> 0x00000000/0x0000 BKT Prot ___Source IP/port____ ____Dest. IP/port____ Tot_pkt/bytes Pkt/Byte Drp 0 tcp 192.168.56.1/33547 192.168.56.4/80 238083 134515909 0 0 623
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