[COFF] Terminology query - 'system process'?

[Paul Winalski]

For me, the term "system process" means either:

o A conventional, but perhaps privileged user-mode process that
performs a system function.  An example would be the output side of a
spooling system, or an operator communications process.

o A process, or at least an address space + execution thread, that
runs in privileged mode on the hardware and whose address space is in
the resident kernel.

Do Unix system processes participate in time-sliced scheduling the way
that user processes do?

On 12/14/23, Bakul Shah <bakul at iitbombay.org> wrote:
>
> Exactly! If blocking was not required, you can do the work in an
> interrupt handler. If blocking is required, you can't just use the
> stack of a random process (while in supervisor mode) unless you
> are doing some work specifically on its behalf.
>
>> Interestingly, other early systems don't seem to have thought of this
>> structuring technique.
>
> I suspect IBM operating systems probably did use them. At least TSO
> must have. Once you start *accounting* (and charging) for cpu time,
> this idea must fall out naturally. You don't want to charge a process
> for kernel time used for an unrelated work!

The usual programming convention for IBM S/360/370 operating systems
(OS/360, OS/VS, TOS and DOS/360, DOS/VS) did not involve use of a
stack at all, unless one was writing a routine involving recursive
calls, and that was rare.  Addressing for both program and data was
done using a base register + offset.  PL/I is the only IBM HLL I know
that explicitly supported recursion.  I don't know how they
implemented automatic variables assigned to memory in recursive
routines.  It might have been a linked list rather than a stack.

I remember when I first went from the IBM world and started
programming VAX/VMS, I thought it was really weird to burn an entire
register just for a process stack.

> There was a race condition in V7 swapping code. Once a colleague and I
> spent two weeks of 16 hour debugging days!

I had a race condition in some multithread code I wrote.  I couldn't
find it the bug.  I even resorted to getting machine code listings of
the whole program and marking the critical and non-critical sections
with green and red markers.  I eventually threw all of the code out
and rewrite it from scratch.  The second version didn't have the race
condition.

-Paul W.