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From: barmar@think.com (Barry Margolin)
Newsgroups: comp.unix.wizards
Subject: Stopped processes with negative priority
Message-ID: <1991May16.062850.14385@Think.COM>
Date: 16 May 91 06:28:50 GMT
Sender: news@Think.COM
Organization: Thinking Machines Corporation, Cambridge MA, USA
Lines: 24
Originator: barmar@gandalf.think.com

From time to time I notice stopped processes with negative priority
(perhaps always -5, in case this is significant) on our Sun-4's (running
SunOS 4.1.1, but I think I remember seeing this in earlier SunOS releases
as well).  I generally notice it because any process with a negative
priority is included in the load average, and the load sometimes gets
pinned at 1.5-2 even though no processes are running hard.  If I send the
process a SIGCONT it immediately stops again, but this time with a positive
priority, so the load goes down to a reasonable level.

I suspect that the problem may be a kernel race condition.  The processes
in this state always seem to be full screen programs.  I suspect what's
happening is that the program catches SIGTSTP, resets tty modes, and then
sends itself a SIGSTOP to stop itself for real.  Maybe the process is being
stopped before the kernel has restored the priority.

Is this indicative of a real problem?  Are these processes using any more
system resources than ordinary stopped processes?  If they're counted in
the load average, then I assume this means that they're sitting on the
active process queue, so are they increasing the scheduler overhead?
-- 
Barry Margolin, Thinking Machines Corp.

barmar@think.com
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