13 Nov
2022
13 Nov
'22
2:52 a.m.
On Sun, Nov 13, 2022 at 12:12:32PM +1100, Rob Pike wrote:
See
https://github.com/plan9foundation/plan9/blob/main/sys/src/9/port/proc.c
for instance - almost all of sched is bookkeeping and a comment about
locks. The little burst at the bottom, starting around line 163, that does
the work is so compact. (setlabel and gotolabel are setjmp and longjmp.)
This reminds me of code I did for Udi Manber as a grad (or undergrad)
student. He wanted a user space threads library so I wrote one.
It's where I learned how to write swtch() where you enter as one thread
and exit as another one. 99% of the code was C that did all the stuff
you could do in C and then a small amount of assembler that did the flip.
I had heard that swtch() was hard but it really isn't that bad.
The assembler makes you learn that stuff but you need to know that stuff
anyway. I do agree with people who say you aren't a kernel engineer if
you haven't written, or at least understood, that code.