Re: [9fans] Getting started in Plan9 - help

["Russ Cox" <rsc@plan9.bell-labs.com>]

First of all, I was kidding about readline.

> * If dynamic linked libraries, you have taken the first step
>   on the slippery slope to the land of gratuitious complexity,
>   where even a simple "hello, world" C program can execute
>   100000 instructions before it actually prints anything.
>   (No, I'm not kidding.)  For some reason, people seem to think
>   adding features in dynamic libraries is "free".

If I'm running rio on Plan 9, draw a new window, and run
hello world, how many instructions execute before I see
"hello world" on my screen?  Lots and lots, just not many
in the hello world process.  The kernel has to redirect
the write into rio, rio does some lookups to figure out
which window gets the output, libdraw has to walk around
in the font caches, possibly loading the missing letters,
(which is more kernel calls, context switches to kfs,
and execution of the various code in devsd), finally
preparing a "draw string" request for /dev/draw.  Then the
kernel is back.  For simplicity let's assume that the window
is in front of all the others, so memlayer isn't involved.  Now we
clear the background, either with memset or by making
calls to an accelerated vga routine with some busy waits
(still faster than memset, though).  Then we use
per-character calls to memimagedraw to blacken the appropriate
pixels.  And finally we see "hello world" (assuming that we
have direct access to video memory; if not, we've been drawing
in a soft screen and still need to flush the changed portion
out to video memory).

You're still right, of course; dynamic libraries are a
slippery slope for lots of reasons.  My point is that the
overhead of dynamic libraries is not necessarily worse than
the overhead of other system services like the kernel and
the various Plan 9 file servers, just in a different place.
It takes far more than 100,000 instructions to get "hello world"
onto my screen either way.  How you count depends on what
you care to include.

Russ