Moving the kernel to modern C

Posted Mar 3, 2022 8:50 UTC (Thu) by Wol (subscriber, #4433)
In reply to: Moving the kernel to modern C by dvdeug
Parent article: Moving the kernel to modern C

> (And as the IOCCC has shown over the years, #define is an awesome tool for code doing what you think it should do, not what the naive C programmer thinks it's doing.)

What you are *completely* missing, is that most code like you describe does NOT do what it NEEDS to do.

For the application programmer (real or not), throwing hardware at the problem is an acceptable solution.

For the systems programmer, you can't just go out and get a couple of extra MEG of L1 cache. You can't go out and get a couple of extra cache lines.

I date from the years when tomorrow's weather forecast took 20hrs to run. "Who cares if the program takes twice as long?" - that guy would have been fired!

I did a load of work (copying files around, etc) a while back on my computer. Okay, I run a protection-heavy disk stack, but I think my PC spent the next 20 minutes flushing cache. I don't give a monkeys, it was other wise idle and responsive, but there are PLENTY of people out there who HAVE to care.

If you can optimise your code FOR SPEED without having a clue what's going on under the bonnet, you're a better man than I am, gunga din ...

Cheers,
Wol

Moving the kernel to modern C

Posted Mar 3, 2022 23:00 UTC (Thu) by dvdeug (guest, #10998) [Link]

What does any of this have to do with how slow a program is? Lots of fast programs are unreadable; I think it was Code Complete that talked about writing a DES decrypter in C that was easy to read, and speeding it up one hundred times by turning it into an unreadable pile of assembly. The Linux kernel uses a lot of those nightmare defines to get maximal inline speed at the cost of clarity and ease of finding the code running. Operator overloading has zero effect on speed.

> I date from the years when tomorrow's weather forecast took 20hrs to run.

Weather forecasting always wants faster computers to do more detailed and accurate forecasts. The National Hurricane Center mentioned for their hurricane forecasts that they post every four hours, they run various simulations, and one of them takes six hours to run, meaning it's never as up to date as the other simulations.