Date: Wed, 26 Nov 1997 23:01:50 -0800 (PST) From: Tom <tom@sdf.com> To: Charles Mott <cmott@srv.net> Cc: hackers@freebsd.org Subject: Re: Adaptive scheduling Message-ID: <Pine.BSF.3.95q.971126225416.9407A-100000@misery.sdf.com> In-Reply-To: <Pine.BSF.3.96.971126182039.27657A-100000@darkstar.home>
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On Wed, 26 Nov 1997, Charles Mott wrote: > I've been thinking about writing an engine which would adaptively shcedule > packets over a crowded link. The idea would be to schedule packets based > on bandwidth consumption, with both stream and source IP address taken > into account. The idea is to give the light users good response, but slow > down large transfers a little. There might be other scheduling algorithms > also. Very similar idea to Cisco's "fair queueing" queueing strategy. Basically it looks at how many "conversations" are going on, and makes sure none of them dominate the queue. It works really quite. When a particular server was doing a trasnfers a _lot_ of data over a T1 here rtt to that particular system went up to over 400ms and some packet loss, but other systems on the same T1 barely noticed it. Cisco's also do "custom priority" queues, where you define filters that match traffic to various priority levels (ex. high, medium, and low). I wish FreeBSD filters more generic so could be used by such a queueing system. ... > It is not that difficult to schedule outgoing packets, but incoming > traffic is difficult to control. In the case of tcp streams, one > suggestion has been to rewrite the window value on the tcp packets so that > holding back ACKs will slow down the incoming stream after about two > packets or so. Additionally, it is possible to send icmp source quench > packets to try to slow down external sources. I don't know that these > mechanisms will work very well, though. I don't like it. Just setup "fair queuing" or whatever on all systems on your physical network. After all, whatever inbound traffic you get, came out of something. > I would be interested to hear other ideas on the subject. > > Charles Mott > > > Tom
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