genode/base/include/base/affinity.h

/*
 * \brief  Representation of CPU affinities
 * \author Norman Feske
 * \date   2013-08-07
 */

/*
 * Copyright (C) 2013 Genode Labs GmbH
 *
 * This file is part of the Genode OS framework, which is distributed
 * under the terms of the GNU General Public License version 2.
 */

#ifndef _INCLUDE__BASE__AFFINITY_H_
#define _INCLUDE__BASE__AFFINITY_H_

namespace Genode {

	/**
	 * Affinity to CPU nodes
	 *
	 * The entity of CPU nodes is expected to form a grid where the Euclidean
	 * distance between nodes roughly correlate to the locality of their
	 * respective resources. Closely interacting processes are supposed to
	 * perform best when using nodes close to each other. To allow a relatively
	 * simple specification of such constraints, the affinity of a subsystem
	 * (e.g., a process) to CPU nodes is expressed as a rectangle within the
	 * grid of available CPU nodes. The dimensions of the grid are represented
	 * by 'Affinity::Space'. The rectangle within the grid is represented by
	 * 'Affinity::Location'.
	 */
	class Affinity
	{
		public:

			class Location;

			/**
			 * Bounds of the affinity name space
			 *
			 * An 'Affinity::Space' defines the bounds of a Cartesian
			 * coordinate space that expresses the entity of available CPU
			 * nodes. The dimension values do not necessarily correspond to
			 * physical CPU numbers. They solely represent the range the
			 * 'Affinity::Location' is relative to.
			 */
			class Space
			{
				private:

					unsigned _width, _height;

				public:

					Space() : _width(0), _height(0) { }

					/**
					 * Construct a two-dimensional affinity space
					 */
					Space(unsigned width, unsigned height)
					: _width(width), _height(height) { }

					/**
					 * Constuct one-dimensional affinity space
					 */
					Space(unsigned size) : _width(size), _height(1) { }

					unsigned width()  const { return _width; }
					unsigned height() const { return _height; }
					unsigned total()  const { return _width*_height; }

					/**
					 * Return location of a single CPU of specified index
					 */
					inline Location location_of_index(int index);
			};


			/**
			 * Location within 'Space'
			 */
			class Location
			{
				private:

					int      _xpos,  _ypos;
					unsigned _width, _height;

				public:

					/**
					 * Default constructor creates invalid location
					 */
					Location() : _xpos(0), _ypos(0), _width(0), _height(0) { }

					/**
					 * Constructor to express the affinity to a single CPU
					 */
					Location(int xpos, unsigned ypos)
					: _xpos(xpos), _ypos(ypos), _width(1), _height(1) { }

					/**
					 * Constructor to express the affinity to a set of CPUs
					 */
					Location(int xpos, int ypos, unsigned width, unsigned height)
					: _xpos(xpos), _ypos(ypos), _width(width), _height(height) { }

					int      xpos()   const { return _xpos; }
					int      ypos()   const { return _ypos; }
					unsigned width()  const { return _width; }
					unsigned height() const { return _height; }
					bool     valid()  const { return _width*_height > 0; }
			};

		private:

			Space    _space;
			Location _location;

		public:

			Affinity(Space const &space, Location const &location)
			: _space(space), _location(location) { }

			Affinity() { }

			Space    space()    const { return _space; }
			Location location() const { return _location; }

			/**
			 * Return location scaled to specified affinity space
			 */
			Location scale_to(Space const &space) const
			{
				if (_space.total() == 0)
					return Location();

				/*
				 * Calculate coordinates of rectangle corners
				 *
				 * P1 is the upper left corner, inside the rectangle.
				 * P2 is the lower right corner, outside the rectangle.
				 */
				int const x1 = _location.xpos(),
				          y1 = _location.ypos(),
				          x2 = _location.width()  + x1,
				          y2 = _location.height() + y1;

				/* scale corner positions */
				int const scaled_x1 = (x1*space.width())  / _space.width(),
				          scaled_y1 = (y1*space.height()) / _space.height(),
				          scaled_x2 = (x2*space.width())  / _space.width(),
				          scaled_y2 = (y2*space.height()) / _space.height();

				/* make sure to not scale the location size to zero */
				return Location(scaled_x1, scaled_y1,
				                max(scaled_x2 - scaled_x1, 1),
				                max(scaled_y2 - scaled_y1, 1));
			}
	};


	Affinity::Location Affinity::Space::location_of_index(int index)
	{
		return Location(index % _width, index / _width, 1, 1);
	}
}

#endif /* _INCLUDE__BASE__AFFINITY_H_ */