4.2 scheduler

[Greg Noel]

In article <893 at psivax.UUCP> friesen at psivax.UUCP (Stanley Friesen) writes:
>	I don't really know, but I suspect that specialized,
>tailor-made support code is going to be more efficient than the
>generalized support available from the kernel.

Er, no.  There are two reasons why not.  First, "tailor-made" support code
is often \less/ efficient than the corresponding general-but-highly-optimized
code in the kernel simply because more attention has been paid to making it
efficient, and secondly, a global resource manager can often make \better/
decisions than a local, narrowly-focused one.  That's why you are willing to
"pay" for such services -- it may not be quite as optimal for the individual
user, but it gives better system-level performance.

The concept that it can be more efficient to expend cycles in the kernel seems
to be a difficult one for a lot of people to comprehend.  I once argued this
point with Grace Hooper and could never get her to accept that anything run in
kernel mode (really, anything that turned on the supervisor-state light on the
360 panel) could be anything but overhead.  I suspect that this is because on
an IBM-class operating system, where the user program has to carry around all
the access routines and run them in user mode, most of the supervisor-state
code \is/ overhead.  'Tain't so with Unix and to blindly apply the same methods
to measure "efficiency" is to end up comparing apples and oranges.
-- 
-- Greg Noel, NCR Rancho Bernardo    Greg at ncr-sd.UUCP or Greg at nosc.ARPA