Path: utzoo!attcan!uunet!cs.utexas.edu!sun-barr!olivea!orc!inews!cmdnfs!bhoughto
From: bhoughto@cmdnfs.intel.com (Blair P. Houghton)
Newsgroups: comp.sys.apollo
Subject: Re: Process Priorities
Message-ID: <545@inews.intel.com>
Date: 22 Oct 90 15:41:28 GMT
References: <9010220501.AA09206@pan.ssec.honeywell.com>
Sender: news@inews.intel.com
Organization: Intel Corp, Chandler, AZ
Lines: 43

In article <9010220501.AA09206@pan.ssec.honeywell.com> thompson@PAN.SSEC.HONEYWELL.COM (John Thompson) writes:
>What we would like is a mechanism that gives out cpu time to all intensive 
>jobs, not just the high-priority ones.  If process priorities aged while
>they were INVOLUNTARILY swapped out, we could probably find a set of
>priorities that gave the approximate percentages.
>
>Am I mistaken, or do _real_ unix priorities age the way I want DomainOS
>priorites to?

Well, semantically, there is no _real_ unix, only various flavors
of frozen-yogurt unix...

BSD4.3, according to "The Design and Implementation of the 4.3BSD
UNIX(R) Operating System" by S. J. Leffler, et al, computes process
priority thusly:

	p_usrpri = PUSER + p_cpu/4 + 2*p_nice

where
	PUSER	is the offset between system and user priority as
		compiled into the kernel
	p_cpu	is the CPU utilization:  the time, in clock-ticks
		(1 per millisecond, usually), that the process
		has been in the RUN state
	p_nice	is the nice value as assigned (in your case,
		either 0 or -5)

p_cpu does "age"; it decays according to the following formula
which is computed once per second for each process in the queues:

	p_cpu = p+nice + p_cpu * (2*load)/(1 + 2*load)

where
	load	is an average of the run-queue length over the
		past minute

That's what "real" unix does.  I don't even know enough about
my Apollos yet to find the priority, so I can't compare the
computations, myself...

				--Blair
				  "All's I need's a good binary editor
				   and a brand new copy of cc..."