Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!fluke!jeff
From: jeff@tc.fluke.COM (Jeff Stearns)
Newsgroups: comp.dcom.modems
Subject: Re: Telebit transfer rate problem
Message-ID: <7457@fluke.COM>
Date: 28 Mar 89 00:01:10 GMT
References: <640@island.uu.net>
Sender: news@tc.fluke.COM
Organization: John Fluke Mfg. Co., Inc., Everett, WA
Lines: 25

In article <640@island.uu.net> brad@island.uu.net (Bradley Mabe) writes:
>We seem to be having a curious problem with our telebit modems.
>When connecting to another site via uucp in pep mode we get an average 
>send rate of around 1200 bytes per second, but and average receive rate 
>of only 500 bytes per second. The modems are connected to a sun 2/170 via 
>a 16 channel systec multiplexer and we are running sunOS 3.2. ...

You have discovered that the Sun kernel burns a lot of cycles servicing
interrupts from the Systech serial interface when performing raw input.
You can confirm this by running vmstat while uucico is receiving files;
note the very high percentage of system time.

Sun has known this for quite some time.  I doubt that they'll ever do anything
more about it; they probably feel that the hardware is nearly obsolete.

When I pointed this problem out to Sun in 1987, they suggested that I upgrade
to a Sun-3 and run run a custom device driver for ttya or ttyb.  (I believe
that they called it "CONSULT-HISPEED".)  This "solution" wasn't viable for us,
so I can't report on whether it works or not.
-- 
    Jeff Stearns        John Fluke Mfg. Co, Inc.               (206) 356-5064
    jeff@tc.fluke.COM   {uw-beaver,microsoft,sun}!fluke!jeff
						  
PS - Calling all users of the Vitalink TransLAN IV Ethernet bridge! Please
     drop me a line.