Leinux tristone13th

When does Linux KVM emulate instructions?

Flow Chart

graph LR

x86_emulate_instruction --> x86_emulate_insn
emulate_instruction --> x86_emulate_instruction

vsock notes

about vsocks

Vsocks are a means of providing socket communication (either stream or datagram) directly between VMs and their host operating system. The host and each VM have a 32 bit CID (Context IDentifier) and may connect or bind to a 32 bit port number. Ports < 1024 are privileged ports.

Vsock communication between VMs does not seem to work.
Only one vsock device per VM is supported.

Seamlessly editing remote files in (Neo)Vim with Netrw and scp

Neovim and Vim both come bundled with a standard plugin called Netrw. Netrw acts a file explorer (similar to NERDTree), but more importantly has the ability to work with scp (as well as sftp, rcp, ftp, and lots of others :h netrw-nread) to let you edit files and browse directories that are hosted on a remote machine, inside of your local Vim instance.

This is useful since you are able to use your Vim setup and plugins without copying over your dotfiles to the remote machine. As well, since the file is copied to your local machine, there will be no delay when typing.

Setup

This is optional for Vim, but required for Neovim (check this Neovim issue explaining why).

原文：运维帮

转自：http://linuxperf.com/?p=142

作者：VMUNIX，已授权运维帮转发

/proc/meminfo是了解Linux系统内存使用状况的主要接口，我们最常用的”free”、”vmstat”等命令就是通过它获取数据的，/proc/meminfo所包含的信息比”free”等命令要丰富得多，然而真正理解它并不容易，比如我们知道”Cached”统计的是文件缓存页，manpage上说是“In-memory cache for files read from the disk (the page cache)”，那为什么它不等于[Active(file)+Inactive(file)]？AnonHugePages与AnonPages、HugePages_Total有什么联系和区别？很多细节在手册中并没有讲清楚，本文对此做了一点探究。

负责输出/proc/meminfo的源代码是：fs/proc/meminfo.c : meminfo_proc_show()

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             
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs

Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs

	# https://clang.llvm.org/docs/ClangFormat.html
	# https://clang.llvm.org/docs/ClangFormatStyleOptions.html
	---
	Language: Cpp
	AlignAfterOpenBracket: Align
	AlignConsecutiveAssignments: false # although we like it, it creates churn
	AlignConsecutiveDeclarations: false
	AlignEscapedNewlinesLeft: true
	AlignOperands: true
	AlignTrailingComments: false # churn

	# --------
	# Hardware
	# --------

	# Opcode - operational code
	# Assebly mnemonic - abbreviation for an operation

	# Instruction Code Format (IA-32)
	# - Optional instruction prefix
	# - Operational code

	#!/bin/bash

	# Script for installing Fish Shell on systems without root access.
	# Fish Shell will be installed in $HOME/local/bin.
	# It's assumed that wget and a C/C++ compiler are installed.

	# exit on error
	set -e

	FISH_SHELL_VERSION=2.1.1