Path: utzoo!mnetor!uunet!husc6!rutgers!ucsd!ucbvax!UHHEPG.BITNET!RALPH
From: RALPH@UHHEPG.BITNET
Newsgroups: comp.os.vms
Subject: Re: Wild processes Consuming CPU
Message-ID: <8802072303.AA14347@ucbvax.Berkeley.EDU>
Date: 6 Feb 88 23:21:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 48

Date:  6-FEB-1988 14:45:29.94
From: Ralph Becker-Szendy RALPH AT UHHEPG
To:   0::"info-vax@kl.sri.com",RALPH
Subj: Re: Wild processes Consuming CPU
> Date:         Tue, 5 Jan 88 11:44:00 CDT
> From:         Z919016@UTMBEACH
> Subject:      Wild Processes Consuming CPU
>
> Has this happened to any else?  We have a VAX 750 running
> VMS 4.5.  Twice in the last 3 months, a process has run
> wild and consumed hours of CPU time until noticed and
> killed (this occurs during low-use hours).
>
> First process was in FOCUS, a database package.  Second
> process was in MAIL, and in addition to 2 hours 28 minutes
> of CPU time used in 2 1/2 hours, had a Buffered I/O count
> of over one million.  In both cases, the users had
> gone home, and hadn't done anything unusual.

Yes, on a VT100 connected via 500 ft of cable to a 780 using all modem control
lines. The user switches his terminal off without logging off (staying in DCL).
Then the process starts using around 6% of the available CPU time (absolutely
constant, not just on the average) and creating several IOs per second. As the
process is using CPU time, it is not going to be automatically terminated by
the WATCHER program.

The funny part is: there is no image being executed, it is just DCL; but the
CPU time is being used in USER mode, not on the interrupt-stack, or in kernel
mode. To cure the problem, i just switch the terminal back on, it immediately
stops using CPU time, and it is still in DCL. Also, if the user logs out BEFORE
switching the terminal off, nothing funny happens.

All this happens only with this one terminal, using this one cable, but
on any port with modem control lines.

We don't really understand the problem, but i have the following theory: When
the terminal goes off, its V24 line drivers are not actively driving the modem
control lines any more, so they pick up electrical noise. Actually, we can see
a lot of AC noise on all the output lines of this terminal (around 2V p-p).
Maybe the input lines on the VAX port are too sensitive, and actually register
the noise as being modem control lines changing their state at around 60 Hz,
and this drives the terminal driver crazy. I just don't understand how logging
off could cure this problem. But probably my theory is completely wrong.

Ralph Becker-Szendy                                     RALPH@UHHEPG.BITNET
University of Hawaii / High Energy Physics Group              (808)948-7391
Watanabe Hall #203, 2505 Correa Road, Honolulu, HI 96822
"Hawaii - it's not just for tourists. People actually live and work there."