Parker Lusk plusk01

CPU Affinity

In a single core system, the OS allows multiple processes to run by sharing CPU time with the multiple processes. This is called concurrency, which gives the illusion of multiple processes executing at once, but is in fact just using a scheduler to give each process dedicated time on the CPU. The time associated with switching processes on a single core is overhead caused by context switching.

When a multi-core processor is available to an OS (e.g., Linux), the scheduler will do its best to allow processes to run simultaneously (by placing processes on different cores) in addition to running concurrently (different processes on the same core).

To control which core a process runs on, we can tell the scheduler to give a process a certain affinity towards a given set of CPUs.

Using taskset, we can get/set the CPU affinity of a particular process. Consider the following example.

To make Gazebo die sooner, edit the file at /opt/ros/kinetic/lib/python2.7/dist-packages/roslaunch/nodeprocess.py:

Near line 57, change the timeouts to be:

_TIMEOUT_SIGINT  = 0.5 #seconds
_TIMEOUT_SIGTERM = 0.5 #seconds

This will cause ROS to send a kill signal much sooner.

Triple Boot macOS Sierra + Windows 10 + Ubuntu 16.04

Create a triple boot system on a MacBook Pro 10,1 without Bootcampt and without rEFInd.

Order:

Clean Install of macOS Sierra (http://osxdaily.com/2016/09/26/clean-install-macos-sierra/)
Windows 10
Ubuntu 16.04

Error: libusb_open() failed with LIBUSB_ERROR_ACCESS

	#!/bin/bash

	function draw_uniform {
	# generates a random float in [a b)
	# n.b.: a, b must be ints
	a=$1
	b=$2
	echo "$((a+RANDOM%(b-a))).$((RANDOM%999))"
	}

	#!/bin/bash
	# Given a directory with at least one bag file, find the filename with the
	# latest timestamp (%Y-%m-%d-%H-%M-%S) in name and open it with `rqt_bag`.
	# This is particularly useful given a directory of many rosbags that were
	# created via `rosbag record` without an explicit filename.
	# If the files were created with `rosbag record -o <name>`, then <name>
	# will be appended with a timestamp, in which case the latest of these
	# bags can be found with `./lastbag <name>`.
	#
	# Parker Lusk

	void reverse_memcpy(unsigned char* dst, const unsigned char* src, size_t n)
	{
	for (size_t i=0; i<n; ++i)
	dst[n-1-i] = src[i];
	}

	// ----------------------------------------------------------------------------

	sensor_msgs::PointCloud2 cloudmsg;
	cloudmsg.header.stamp = _img->header.stamp;

	#!/bin/bash
	#
	# NetworkManager is trash for robots (periodic scanning causes
	# ~3s latency every 2 minutes). We have disabled Network Manager
	# (systemctl disable network-manager) and network interfaces are
	# now managed via /etc/network/interfaces, with authenticated
	# wireless managed by wpa_supplicant.
	#
	# Your /etc/network/interfaces probably looks like:
	#

	# Use rosbag filter to create a new bag
	#
	# $ bagcut original.bag 0 336 # cuts from 0 to 336s
	#
	# $ bagcut original.bag 50 # new bag starts 50s in
	#
	# $ bagcut original.bag 10 -20 # cuts from 10 to END_TIME-20s
	function bagcut {
	BAG=${1:0:-4}
	OFFSET=$2

	#!/usr/bin/python

	"""
	I'm expecting a YAML file from OpenCV that looks like:

	%YAML:1.0
	K: !!opencv-matrix
	rows: 3
	cols: 3
	dt: d