From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Furniss Date: Wed, 03 Aug 2005 14:04:08 +0000 Subject: Re: [LARTC] HTB and PRIO qdiscs introducing extra latency when output Message-Id: <42F0CED8.1090406@dsl.pipex.com> List-Id: References: <1122460110.8454.11.camel@pgala.it.nuigalway.ie> In-Reply-To: <1122460110.8454.11.camel@pgala.it.nuigalway.ie> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: lartc@vger.kernel.org Jonathan Lynch wrote: > I did the same tests that I outlined earlier, but this time by setting > hysteresis to 0. The config for the core router is included at the > bottom. The graphs for the delay of the voip stream and the traffic > going through the core router can be found at the following addresses. > > http://140.203.56.30/~jlynch/htb/core_router_hysteresis.png > http://140.203.56.30/~jlynch/htb/voip_stream_24761_hysteresis.png > > > The max delay of the stream has dropped to 1.8ms. Again the jitter seems > to be around 1ms. There seems to be a pattern going whereby the delay > reaches about 1.6ms then drops back to 0.4 ms, jumps back to 1.6ms and > then back to 0.4ms repeatedly and then it rises from 0.5ms gradually and > repeats this behaviour. Is there any explanation to this pattern ? > > Would it have anything go to do with burst being 1ms ? Yes I suppose if you could sample truly randomly you would get a proper distribution - I guess the pattern arises because your timers are synchronised for the test. > > When the ceil is specified as being 90mbit, is this at IP level ? > What does this correspond to when a Mbit = 1,000,000 bits. Im a bit > confused with the way tc interprets this rate. Yes htb uses ip level length (but you can specify overhead & min size) , the rate calculations use a lookup table which is likely to have a granularity of 8 bytes (you can see this with tc -s -d class ls .. look for /8 after the burst/cburst). There is a choice in 2.6 configs about using CPU/jiffies/gettimeofday - I use CPU and now I've got a ping that does < 1 sec I get the same results as you. > > If the ceil is based at IP level then the max ceil is going to be a > value between 54 Mbit and 97 Mbit (not the tc values) for a 100 Mbit > interface depending on the size of the packets passing through, right ? > > Minimum Ethernet frame > 148,809 * (46 * 8) = 148,809 * 368 = 54,761,712 Mbps > > Maximum Ethernet frame > 8,127 * (1500 * 8) = 8,127 * 12,000 = 97,524,000 Mbps If you use the overhead option I think you will be to overcome this limitation and push the rates closer to 100mbit. > About the red settings, I dont understand properly how to configure the > settings. I was using the configuration that came with the examples. I don't use red it was just something I noticed - maybe making it longer would help, maybe my test wasn't rerpresentative. FWIW I had a play around with HFSC (not that I know what I am doing really) and at 92mbit managed to get - rtt min/avg/max/mdev = 0.330/0.414/0.493/0.051 ms loaded from rtt min/avg/max/mdev = 0.114/0.133/0.187/0.028 ms idle and that was through a really cheap switch. Andy. _______________________________________________ LARTC mailing list LARTC@mailman.ds9a.nl http://mailman.ds9a.nl/cgi-bin/mailman/listinfo/lartc