Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!mcvax!ukc!cam-cl!scc From: scc@cl.cam.ac.uk (Stephen Crawley) Newsgroups: comp.os.minix Subject: Re: Re: Amoeba on Token Ring Message-ID: <776@scaup.cl.cam.ac.uk> Date: 5 Jun 89 13:13:47 GMT References: <16240@louie.udel.EDU> <760@scaup.cl.cam.ac.uk> <762@scaup.cl.cam.ac.uk> <2674@sater.cs.vu.nl> Sender: news@cl.cam.ac.uk Distribution: comp Organization: U of Cambridge Comp Lab, UK Lines: 38 In <2674@sater.cs.vu.nl> Hans van Staveren writes: >I do not like to react as hurt in my feelings, but there is no way that the >current Amoeba software will ever generate a broadcast storm. There is special >code to prevent, even in pathological cases like fast client and slow server, >the occurence of more than ~20 broadcasts per second. I do not say that this >is very little, but it only occurs in pretty strange cases, and it will most >certainly not bring an Ethernet to it's knees. The special code that Hans described to me as code to limit the Amoeba TP driver to sending at most one locate broadcast per (10Hz) clock tick. In other words a single kernel can in theory emit 10 broadcast packets per second. I cannot see how this makes a broadcast storm impossible! Sure a single machine won't do it, but if you write a distributed application that does a lot of communication between a number of machines ... watch out! The pathological cases that Hans talks about that are not at all unusual if you naively try to use Amoeba TP as a "universal" transport protocol as some of the the Amoeba proponents claim you can do. For example if you try to build a niave byte stream on top of TP. This is exactly how the CWI supplied amoeba runtime libraries implement stdio streams! I remember being boggled by how slow single character writes to an unbuffered stream were. Now I think I know why.] >Our installation here runs some 40 Amoeba poolprocessors, mostly 68020's, >on the same Ethernet as lots of Sun's and various other stuff. Had it been >that bad someone would certainly have complained to me. Hans: How many Xerox InterLisp machines do you have? Machines like Suns have decent ethernet interfaces and fast processors and can tolerate a surprisingly high broadcast rate. A Xerox 6085 / 1186 has a wimpy ethernet interface and a slow processor and is badly effected by a relatively low broadcast rate. My workstation is a 6085 ... Also, what sort of parallel applications are you running on your 40 pool processors? Were they written by novices or by people (like you) who knew all about the pitfalls of locates?