From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Furniss Date: Wed, 19 May 2004 10:58:17 +0000 Subject: Re: [LARTC] SFQ latency Message-Id: <40AB3DC9.9010403@dsl.pipex.com> List-Id: References: <200405191221.30730.haden@homelan.lt> In-Reply-To: <200405191221.30730.haden@homelan.lt> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: lartc@vger.kernel.org Tomas Simonaitis wrote: > Anyone notices that using sfq qdisc adds latency compared to pfifo? > > With "sfq perturb 10" ping latency is around 100-120ms, while with "pfifo > limit 3" drops to ~10-30ms (qdiscs belong to htb class). > > I'm missing something or is this expected? > > { > $TC_CLASS parent 1:1 classid 1:20 htb prio 0 rate 900kbit ceil 1000kbit burst > 7k > $TC_QDISC parent 1:20 handle 200: {pfifo limit 3} | {sfq perturb 10} > } There shouldn't really be a queue as such (you still choose one) for your interactive traffic - if you really care about latency HTB should have a class with a high (low number) prio and a high rate (> expected traffic), so other traffic has to borrow. If you do end up queueing your interractive, then pfifo limit 3 means there will only be 2 packets in front of the ping (I suppose bfifo would be nicer as a fall back - it will penalise big packets more, WRT drops). SFQ default qlen is 128, though the way it works means the delay will depend on how many other connections are queued. Andy. _______________________________________________ LARTC mailing list / LARTC@mailman.ds9a.nl http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://lartc.org/