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@jboner
jboner / latency.txt
Last active February 6, 2025 21:51
Latency Numbers Every Programmer Should Know
Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference 0.5 ns
Branch mispredict 5 ns
L2 cache reference 7 ns 14x L1 cache
Mutex lock/unlock 25 ns
Main memory reference 100 ns 20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy 3,000 ns 3 us
Send 1K bytes over 1 Gbps network 10,000 ns 10 us
Read 4K randomly from SSD* 150,000 ns 150 us ~1GB/sec SSD
@eyecatchup
eyecatchup / git-commit-log-stats.md
Last active February 6, 2025 14:35
Some commands to get git commit log statistics for a repository on the command line.

git commit stats

Commands to get commit statistics for a Git repository from the command line -
using git log, git shortlog and friends.




@shafik
shafik / WhatIsStrictAliasingAndWhyDoWeCare.md
Last active February 6, 2025 09:18
What is Strict Aliasing and Why do we Care?

What is the Strict Aliasing Rule and Why do we care?

(OR Type Punning, Undefined Behavior and Alignment, Oh My!)

What is strict aliasing? First we will describe what is aliasing and then we can learn what being strict about it means.

In C and C++ aliasing has to do with what expression types we are allowed to access stored values through. In both C and C++ the standard specifies which expression types are allowed to alias which types. The compiler and optimizer are allowed to assume we follow the aliasing rules strictly, hence the term strict aliasing rule. If we attempt to access a value using a type not allowed it is classified as undefined behavior(UB). Once we have undefined behavior all bets are off, the results of our program are no longer reliable.

Unfortunately with strict aliasing violations, we will often obtain the results we expect, leaving the possibility the a future version of a compiler with a new optimization will break code we th

@jkstill
jkstill / proc_net_tcp_decode
Last active January 18, 2025 04:34
decode entries in /proc/net/tcp
Decoding the data in /proc/net/tcp:
Linux 5.x /proc/net/tcp
Linux 6.x /proc/PID/net/tcp
Given a socket:
$ ls -l /proc/24784/fd/11
lrwx------ 1 jkstill dba 64 Dec 4 16:22 /proc/24784/fd/11 -> socket:[15907701]
@Grinnz
Grinnz / perl7faq.md
Last active January 16, 2025 05:59
Perl 7 FAQ

Perl 7 FAQ

last updated 2025-01-16

Is Perl 7 coming?

It has been the plan that this version number will be used for Perl at some point in the future.

As of 2025, there is now a proposal to use the second component of the Perl version number as the major version, skipping over the question of what Perl 7 should or should not be.

require "try-catch"
try {
function()
error('oops')
end,
catch {
function(error)
print('caught error: ' .. error)
@panzi
panzi / portable_endian.h
Last active August 9, 2024 13:12
This provides the endian conversion functions form endian.h on Windows, Linux, *BSD, Mac OS X, and QNX. You still need to use -std=gnu99 instead of -std=c99 for gcc. The functions might actually be macros. Functions: htobe16, htole16, be16toh, le16toh, htobe32, htole32, be32toh, le32toh, htobe64, htole64, be64toh, le64toh. License: I hereby put …
// "License": Public Domain
// I, Mathias Panzenböck, place this file hereby into the public domain. Use it at your own risk for whatever you like.
// In case there are jurisdictions that don't support putting things in the public domain you can also consider it to
// be "dual licensed" under the BSD, MIT and Apache licenses, if you want to. This code is trivial anyway. Consider it
// an example on how to get the endian conversion functions on different platforms.
#ifndef PORTABLE_ENDIAN_H__
#define PORTABLE_ENDIAN_H__
#if (defined(_WIN16) || defined(_WIN32) || defined(_WIN64)) && !defined(__WINDOWS__)
@knazarov
knazarov / full_text_search_tarantool.lua
Created September 23, 2020 08:00
Full text search example for Tarantool
#!/usr/bin/env tarantool
local pickle = require('pickle')
local yaml = require('yaml')
function trivec(str)
str = string.lower(str)
local vec = ""

See synthesized write-up here

  • Do a quick performance check in 60 seconds
  • Use a number of different tools available in unix
  • Use flamegraphs of the callstack if you have access to them
  • Best performance winds are elimiating unnecessary wrok, for example a thread stack in a loop, eliminating bad config
  • Mantras: Don't do it (elimiate); do it again (caching); do it less (polling), do it when they're not looking, do it concurrently, do it more cheaply