Return to BSD News archive
Newsgroups: comp.os.386bsd.questions Path: sserve!newshost.anu.edu.au!harbinger.cc.monash.edu.au!news.mira.net.au!news.netspace.net.au!serval.net.wsu.edu!netnews.nwnet.net!oracle.pnl.gov!osi-east2.es.net!lll-winken.llnl.gov!noc.near.net!monk.proteon.com!jfw From: jfw@proteon.com (John Woods) Subject: Re: What is a "silo overflow"? Message-ID: <D2vGKr.op@proteon.com> Sender: news@proteon.com Nntp-Posting-Host: hendrix.proteon.com Organization: Proteon, Inc., Westborough, Ma. References: <3fn18a$gej@sundog.tiac.net> Date: Mon, 23 Jan 1995 18:55:39 GMT Lines: 25 umar@tiac.net (Rob Landry) writes: >I'm running nn under NetBSD 1.0. Every once in a while I get a message >that says "silo overflow". There don't seem to be any measurable consqeuen- >ces of these messages. >What is a "silo overflow"? Should I be doing anything to prevent or elimi- >nate them? A silo overflow happens when 17 characters attempt to accumulate in the 16-character silo buffer in a 16550AF chip. If you're running SLIP or PPP, the consequence will be a packet getting tossed because of the character getting tossed, which will then cause a TCP timeout/retry (assuming it's a TCP packet that got hammered). To prevent them, you can get a MUCH, MUCH faster computer :-). On my home system, I'm experimenting with reducing the FIFO interrupt trigger point from 8 to 4, hoping that this prevents character loss and thus makes up in avoided TCP retransmissions what I lose in (possibly) increased interrupt overhead. (That requires editing the com.c driver.) I've seen no further drops in a day of not terribly extensive testing. It is possible that the origin of the dropped characters isn't in the com.c driver (which, nevertheless, deserves to be taken out back and shot); something *else* may be periodically holding onto the interrupt disable long enough for characters to be dropped. There is nothing the com.c driver could do about that (unless said hogging lasts only 9 character times, in which case changing the threshhold will take care of it).