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From: Larry McVoy <lm@mcvoy.com>
To: Rob Pike <robpike@gmail.com>
Cc: The Eunuchs Hysterical Society <tuhs@tuhs.org>
Subject: [TUHS] Re: Book: "You Are Not Expected to Understand This"
Date: Sat, 12 Nov 2022 17:52:59 -0800	[thread overview]
Message-ID: <20221113015259.GJ9823@mcvoy.com> (raw)
In-Reply-To: <CAKzdPgzAPB+-LjtZ+rhqRY8+Cdk4Fqks5hK1EdmShT_QbGHKjg@mail.gmail.com>

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.

  reply	other threads:[~2022-11-13  1:53 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-13  0:02 [TUHS] " Dave Horsfall
2022-11-13  0:25 ` [TUHS] " Kenneth Goodwin
2022-11-13  1:12   ` Rob Pike
2022-11-13  1:52     ` Larry McVoy [this message]
2022-11-13  1:12 ` Stuff Received
2022-11-13 21:58   ` Dave Horsfall
2022-11-14 22:48 ` Dave Horsfall
2022-11-14 14:14 Douglas McIlroy
2022-11-14 15:50 ` Clem Cole
2022-11-14 16:58 Norman Wilson
2022-11-14 19:17 ` Larry McVoy
2022-11-14 19:50   ` Dave Horsfall

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