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 |
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
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] |
last updated 2025-01-16
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) |
// "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__) |
#!/usr/bin/env tarantool | |
local pickle = require('pickle') | |
local yaml = require('yaml') | |
function trivec(str) | |
str = string.lower(str) | |
local vec = "" |
- 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