Beautiful Code Exists,
If You Know Where to Look
Coding is his game, pleasantries distained.
I’ve been reading your rants in Queue
for a while now and I can’t help asking, is there any code you do like? You
always seem so negative; I really wonder if you actually believe the world of
programming is such an ugly place or if
there is, somewhere, some happy place
that you go to but never tell your readers about.
a happy Programmer
Dear mr. happy,
While I will try not to take exception
to your calling my writings “rants,” I
have to say that I am surprised by your
question. KV is a happy, cheerful, outgoing kind of guy who not only has a
“happy place,” but also carries it with
him wherever he goes, sharing joy and
laughter with everyone around him
and giving sweets to small children.
Now that I’ve bleached my brain,
I can answer a bit more honestly. Yes,
in fact, there are good systems and I
have seen good code, sometimes even
great code, in my time. I would like to
describe one such chunk of good code
right now. Unfortunately, it will require
a bit of background to explain what
the code is, but please stick with me.
Perhaps you can relax by going to your
“happy place” first.
One of my recent projects has been
to extend support for something called
hardware performance monitoring
counters (hwpmc) on FreeBSD, the op-
erating system I work on. As the name
indicates, hwpmc is implemented in
hardware, and in this case hardware
means on the CPU. I don’t know if
you’ve ever read CPU or chip documentation, but there is little in our industry that is more difficult to write or less
pleasant to read. It’s bad enough that
the subject is as dry as the surface of
the moon, but it’s much worse because
the people who write such documentation either don’t understand the technology or are terrible writers, and often
there is a fatal combination of the two.
Starting from that base, the typical
software engineer produces code that
somewhat mirrors the specification,
and as things that grow in poison soil
themselves become poison, the code is
often as confusing as the specification.
What is hwpmc? It is a set of counters that reside on the CPU that can
record various types of events of interest to engineers. If you want to know
if your code is thrashing the L2 cache
or if the compiler is generating sub-optimal code that’s messing up the
pipeline, this is a system you want to
use. Though these things may seem
esoteric, if you’re working on high-performance computing, they’re vitally
important. As you might imagine, such
counters are CPU specific, but not just
by company, with Intel being different from AMD: even the model of CPU
bears on the counters that are present,
as well as how they are accessed.
The sections covering hwpmc in
Intel’s current manual, Intel® 64 and
IA- 32 Architectures Software Developer’s
Manual Volume 3B: System Programming
Guide, Part 2, encompass 249 pages: 81
to describe the various systems on various chips and 168 to cover all the counters you can use on the chips. That’s a
decent-size novel, but of course without the interesting story line. Kudos
to Intel’s tech writers, as this is not the
worst chip manual I have ever read,
but I would still rather have been reading something else. Once I had read
through all of this background material, I was a bit worried about what I
would see when I opened the file.
But I wasn’t too worried, because I
knew the programmer who wrote the
code personally. He’s a very diligent
engineer who not only is a good coder
but also can explain what he has done
and why. When I told him that I would
be trying to add more chip models
to the system he wrote, he sent me a
1,300-word email message detailing
just how to add support for new chips
and counters to the system.
What’s so great about this software?
Well, let’s look at a few snippets of the
code. It’s important to always read the
header files before the code, because
header files are where the structures
are defined. If the structures aren’t defined in the header file, you’re doomed
from the start. Looking at the top of the
very first header file I opened we see the
code snippet shown in Figure 1. Why
do these lines indicate quality code to
me? Is it the capitalization? Spacing?
Use of tabs? No, of course not! It’s the