cperciva

33 ms·

631.
by cperciva 3y ago
All models are wrong, but some models are useful. Asking if the model is wrong is asking the wrong question; the important question is whether it's useful.
632.
by cperciva 3y ago
While I agree about the thermodynamic argument -- you can't extract CO2 from the atmosphere without using significantly more energy than you released by burning fossil fuels -- there's an argument to be made that not all kWh are e
633.
by cperciva 3y ago
Yes, Bouba and Kiki are the same in all languages.
634.
by cperciva 3y ago
Sure, you know a little bit about TCP, just like I know a little bit about EC2, and Paul Graham knows a little bit about startups.
635.
by cperciva 3y ago
Yes, I'm inclined to say that they dodged a bullet there. The BSD community has been dealing with this for decades (which is one of the reasons Beastie is FreeBSD's mascot but not our logo).
636.
by cperciva 3y ago
The story should end there. However, we'd separately come up with the name "PayDemon" and had already purchased both paydemon.com and paydaemon.com (we just couldn't let go of our UNIX references, apparently). Despite b
637.
by cperciva 3y ago
Glucagon should probably be a safety net, not something you use regularly. Taking too much insulin and compensating with glucagon leads to long term weight gain among other things. Dual pumps are being worked on, but it's not yet clea
638.
by cperciva 3y ago
Equivalent but perhaps more catchy: "Pi seconds are a nanocentury".
639.
by cperciva 3y ago
Sure, but that doesn't help me when I want to go into that code and add extras debugging code so I can figure out where things are going wrong.
640.
by cperciva 3y ago
The first thing you'll want to do is port my TSLOG code to the OpenBSD kernel and start instrumenting things there. Send me an email, there's too much detail to get into for an HN comment.
641.
by cperciva 3y ago
Figuring out how to get all the crate source code extracted was the first step, yes. But when after that, the object oriented nature meant that there were often many different foo functions, so I had to dig through the code to figure out
642.
by cperciva 3y ago
I suspect that FreeBSD has fewer pauses than OpenBSD... especially after the work I've done over the past few years to speed it up. If anyone in the OpenBSD world is interested in speeding up your boot process I'd be happy to shar
643.
by cperciva 3y ago
My development environment for this was mostly "nano in an SSH session". (Among other reasons, I can't even build Firecracker locally.) For FreeBSD work that's just fine since grep can find things for me. It didn&#x27
644.
by cperciva 3y ago
Firecracker's source is rather simple and even relatively readable for non-experts. ... as long as they're experienced at writing Rust. As a Rust newbie it took me a long time to figure out simple things like "where is fo
645.
by cperciva 3y ago
Probably a significant proportion of the sysadmins who experienced that one-second pause. The "print a message telling the user that we're rebooting, then wait a second to let them read the console before we go ahead and reboot&qu
646.
by cperciva 3y ago
FWIW, this is basically the same material -- after my BSDCan talk the FreeBSD Journal said "hey, that was a great talk, can you turn it into an article for us", and after the FreeBSD Journal article was published ;login: asked if
647.
FreeBSD on Firecracker: Experiences Porting FreeBSD 14 to the Firecracker VMM(usenix.org)
4 points by cperciva 3y ago|0 comments
648.
by cperciva 3y ago
There are in-place array mergesorts. (Nobody uses them because they're horribly complicated, though.) In this case however I'm putting all of the SYSINITs onto a linked list; mergesorting a linked list is easy.
649.
by cperciva 3y ago
There isn't supposed to be an implicit ordering requirement. But a number of bugs have happened in the past because people didn't order properly. What we need isn't actually "stable" so much as "consistent f
650.
by cperciva 3y ago
Maybe. The tradeoff is that having two different ways of doing something makes it more likely that one will break without anyone noticing.
651.
by cperciva 3y ago
If I get the entire kernel boot down to 1 ms I might take another look at this. ;-) You absolutely can compile everything you need into the kernel -- in fact for Firecracker you have to since you don't have a boot loader handing you mu
652.
by cperciva 3y ago
I believe Linux is at 75-80 ms for the same environment where I have FreeBSD booting in 25 ms. That comes from a Firecracker benchmark which I think is an apples-to-apples comparison with what I'm measuring in FreeBSD, but I'm
653.
by cperciva 3y ago
Options for sorting algorithms are severely limited when (a) you can't use malloc, (b) you don't have enough stack to recurse, and (c) you want a stable sort. (The first two limitations are because this happens very early in the
654.
by cperciva 3y ago
Two reasons: First, it's not worth screwing with the linker to save 20 microseconds. Second, you need to merge lists anyway because kernel modules.
655.
by cperciva 3y ago
The mergesort is roughly 100x faster than the bubblesort was. I made no claim in that tweet about the overall speedup. (But since you mention it, when I started working on speeding up the boot process, the kernel took about 10 seconds to b
656.
by cperciva 3y ago
What is special about the 'wheel' group and what is su even "checking" in the first place? Users who aren't in the wheel group aren't supposed to be able to become root, even if they have the password. Isn&#
657.
by cperciva 3y ago
Yup. The same goes for mathematics programs around the world -- a relatively small number of Math majors, but the departments are kept afloat by teaching calculus courses to everyone going into other science and engineering programs.
658.
by cperciva 3y ago
Students don't just take courses in their own program. What we have here is 61 students majoring in languages, but lots of students from elsewhere in the institution taking language courses. Possibly because of a foreign language r
659.
by cperciva 3y ago
That bootloader needs to mount a filesystem to find the kernel. The kernel needs to mount the filesystem to run the system. Each of those mount operations is done with different code... Not on FreeBSD. Our bootloader reuses kernel code (
660.
by cperciva 3y ago
A classical computer can solve a linear system in O(N) time on O(N^2) processors, too.

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