From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f171.google.com (mail-we0-f171.google.com [74.125.82.171]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client did not present a certificate) by huchra.bufferbloat.net (Postfix) with ESMTPS id AED90200994 for ; Tue, 4 Sep 2012 09:40:43 -0700 (PDT) Received: by weys43 with SMTP id s43so7400968wey.16 for ; Tue, 04 Sep 2012 09:40:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; bh=wN+u1z3bR4gsTo678w7QVLBzN5oXNNXU3dobJKtUioA=; b=y7a4JM11hgMAKtQbGdUoNMSXjwEFjvluRnh1zksi/9rV5rh/I75Zc1zQMF+cKsCkUi vC7R/cVVX8I/9ykLW5mMBSLVklsnMXhdjZV+4S4FlFwPACJklaxBOqc7ookDK8bh3wWi 0NCwnkxaZc7tYBv1Y8GQ9V3Vwdah6z55tGWZO9GcA6oUgrx4GszuRUFTnVC9RfZzxrwr fNt8BPvG8pgH5usLf4eYaoFpisVzcW4TfGdgWzs0mhON6rFzBXtbgQEg+5IZ+FTqzhFN nWEbNskepbxBBtl51yR9m1m0gBAjTOchA1oXu3RnhDSF1khMv9t3OHDpvxQQPlalHE3Q 8u1A== MIME-Version: 1.0 Received: by 10.216.181.67 with SMTP id k45mr11075981wem.17.1346776840961; Tue, 04 Sep 2012 09:40:40 -0700 (PDT) Received: by 10.223.159.134 with HTTP; Tue, 4 Sep 2012 09:40:40 -0700 (PDT) In-Reply-To: <1346772855.13121.40.camel@edumazet-glaptop> References: <1346396137.2586.301.camel@edumazet-glaptop> <1346421031.2591.34.camel@edumazet-glaptop> <1346421466.2591.38.camel@edumazet-glaptop> <1346503884.7996.65.camel@edumazet-glaptop> <1346772855.13121.40.camel@edumazet-glaptop> Date: Tue, 4 Sep 2012 09:40:40 -0700 Message-ID: From: Dave Taht To: Eric Dumazet Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Cc: Tomas Hruby , Nandita Dukkipati , netdev , codel@lists.bufferbloat.net Subject: Re: [Codel] [RFC v2] fq_codel : interval servo on hosts X-BeenThere: codel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: CoDel AQM discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 04 Sep 2012 16:40:44 -0000 On Tue, Sep 4, 2012 at 8:34 AM, Eric Dumazet wrote= : > On Tue, 2012-09-04 at 08:10 -0700, Nandita Dukkipati wrote: >> The idea of using srtt as interval makes sense to me if alongside we >> also hash flows with similar RTTs into same bucket. But with just the >> change in interval, I am not sure how codel is expected to behave. >> >> My understanding is: the interval (usually set to worst case expected >> RTT) is used to measure the standing queue or the "bad" queue. Suppose >> 1ms and 100ms RTT flows get hashed to same bucket, then the interval >> with this patch will flip flop between 1ms and 100ms. How is this >> expected to measure a standing queue? In fact I think the 1ms flow may >> land up measuring the burstiness or the "good" queue created by the >> long RTT flows, and this isn't desirable. Experiments would be good. > > Well, how things settle with a pure codel, mixing flows of very > different RTT then ? Elephants are shot statistically more often than mice. > It seems there is a high resistance on SFQ/fq_codel model because of the > probabilities of flows sharing a bucket. I was going to do this in a separate email, because it is a little off-topi= c. fq_codel has a standing queue problem, based on the fact that when a queue empties, codel.h resets. This made sense for the single FIFO codel but not multi-queued fq_codel. So after we hit X high rate flows, target can never be achieved, even straining mightily, and we end up with a standing queue again. Easily seen with like 150 bidirectional flows at 10 or 100Mbit. (as queues go, it's still pretty good queue. And: I've fiddled with various means of draining multi-queue behavior thus far, and they ended up unstable/unfair) > So what about removing the stochastic thing and switch to a hash with > collision resolution ? Was considered and discarded in the original SFQ paper as being too computationally intensive (in 1993). Worth revisiting. http://www2.rdrop.com/~paulmck/scalability/paper/sfq.2002.06.04.pdf > > --=20 Dave T=E4ht http://www.bufferbloat.net/projects/cerowrt/wiki - "3.3.8-17 is out with fq_codel!"