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From: corwin@bsu-cs.UUCP (Paul Frommeyer)
Newsgroups: comp.os.vms
Subject: Re: bsd unix vs. dec's vms
Message-ID: <696@bsu-cs.UUCP>
Date: Sat, 23-May-87 01:11:41 EDT
Article-I.D.: bsu-cs.696
Posted: Sat May 23 01:11:41 1987
Date-Received: Sat, 23-May-87 19:10:01 EDT
References: <5828@shemp.UCLA.EDU> <34ab0e42.8be4@apollo.uucp> <695@bsu-cs.UUCP>
Organization: CS Dept, Ball St U, Muncie, Indiana
Lines: 57
Summary: VMS process creation from VAX/VMS Internal(Digital Press, 1984)


For the sake of the massive debate raging over the process creation under
DCL, here are the gory details as laid out by Digital themselves in the
VMS internals book:

The creation of a new proces requires the cooperation of several pieces
of the executive.

-Creation begins in the context of an existing process that executes a Create
Process system service call. The Create Process system service performs the
following steps:

a. It makes privilege and quota checks
b. It loads the PCB, possibly the JIB if creating a detached process,
and the process quota block with explicit SYS$CREPRC arguments and implicit
parameters taken from the context of the creator.
c. It places the new process into the scheduler's data base.

-The initial scheduling state of the new ocess is COMO (computable but
outswapped). Thus, execution of the shell process is suppressed until the
swapper process moves the new process into the balance set. The following
steps are performed in the context of the swapper process:

a. The swapper inswaps the template process context from SHELL, a portion
of the executive image SYS.EXE.
b. The process header is built according to the values of SYSBOOT
parameters for this configuration.

-The final steps of process initialization take place in the context
of the new process in a routine called PROCSTRT. PROCSTRT performs
the following steps:

a. The arguments from the PQB are moved to their proper places in the
process header and P1 space.
b. The image activator is called to activate the image.
c. The image is called at its entry poin

There's a whole chapter more of this (Chapter 20), but that's the general
overview. There seems to be something to both mine and Rahul Dhesi's
view based on this evidence (this will teach me to get my facts straight...).
It appears that DCL is only a partial contribution to the slowness of
process creation. While I was right in saying all the data structures are
in memory, the creation of the process in an outswapped state may be what
slows things down. If the creation could be coprocessed, with DMA image
load simultaneous with data structure manipulation, that might speed
things up. Well, if Digital ever hires me like I desperately wish 
then perhaps I'll have an opportunity to learn more about process
manipulation in VMS...

N.B. Apologies for any typos in the above transcript.



-- 
Paul "Corwin" Frommeyer        "Experience is no substitute for competence."
UUCP: 
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