jinyangustc

Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
Syscall on Intel 5150 ...................... 105 ns
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Context switch on Intel 5150 ............. 4,300 ns  =   4 µs

Send 2K bytes over 1 Gbps network ....... 20,000 ns = 20 µs

jinyangustc

import time
import traceback
from typing import Literal, final


class String:
    """
    A variant containing a string
    """

jinyangustc

;; nano-emacs.el --- NANO Emacs (minimal version)     -*- lexical-binding: t -*-

;; Copyright (c) 2025  Nicolas P. Rougier
;; Released under the GNU General Public License 3.0
;; Author: Nicolas P. Rougier <[email protected]>
;; URL: https://github.com/rougier/nano-emacs

;; This is NANO Emacs in 256 lines, without any dependency 
;; Usage (command line):  emacs -Q -l nano.el -[light|dark]

jinyangustc

Do your Raspberry Pi's Network Interfaces freeze?

My Raspberry Pi 4 kept losing its wlan0 interface. I could usually reconnect via Ethernet but, from time to time, I noticed that the eth0 interface would also go walkabout.

I tried a lot of things but the one described here seems to have cured the problem. I have no idea why it works. It just does.

Step 0 - are you a Windows user?

The script shown in the next step should be created on your Raspberry Pi. Please do not make the mistake of selecting the text, copying it into a text editor on your Windows machine, saving the file, and then moving the file to your Raspberry Pi. Unless you take precautions, Windows will add its 0x0d 0x0a (CR+LF) line endings and those will stop the script from working properly on your Raspberry Pi.

jinyangustc

Checking your Raspberry Pi's view of its power supply

Sometimes it seems like the first (and sometimes only) advice you get offered for almost any problem with a Raspberry Pi is "check your power supply". You think something like:

"hey, I'm using an official power supply sold as being matched with my Pi so how can there be any problem?"

You look up the specs then stick a controlled load across your supply and confirm that it can deliver the required number of Watts.

Yet your problems persist…

jinyangustc

System wide cpu usage:

The numbers on the top left from 1 to 8 represents the number of cpu's/cores in my system with the progress bar next to them representing the load of cpu/core. As you would have noticed the progress bars can be comprised of different colors. The following list will explain what each color means.

Blue: low priority processes (nice > 0)
Green: normal (user) processes
Red: kernel processes
Yellow: IRQ time
Magenta: Soft IRQ time
Grey: IO Wait time

jinyangustc

#!/bin/bash

# Script that updates the iTerm Badge with the hostname of the server that you are
# connecting to with ssh.
#
# Instructions:
# - Put this script in ~/bin/ssh (this will override the default ssh binary)
# - Run 'chmod +x ~/bin/ssh' to give execution permission to the script
# - Open iTerm\Preferences\Profiles, select your profile and put '\(user.current_ssh_host)' in the Badge text box
# - Enjoy!

jinyangustc

set nocompatible
filetype indent on
syntax on
set hidden
set wildmenu
set showcmd
set incsearch
set nohlsearch
hi Search ctermbg=Grey
set backspace=indent,eol,start

jinyangustc

{
    "name": "Acme",
    "author": "Adriano Romanazzo (multiversecoder)",
    "globals":
    {
        "foreground": "#000",
        "background": "#FFFEEC",
        "border": "13px solid #000",
        "accent": "#000",
        "caret": "#000",

jinyangustc

How to sort dict...

By value

Return as a list of tuples:

x = {1: 2, 3: 4, 4: 3, 2: 1, 0: 0}
sorted_x = sorted(x.items(), key=lambda kv: kv[1])
#=> [(0, 0), (2, 1), (1, 2), (4, 3), (3, 4)]