genode/repos/base-hw/src/core/kernel/cpu_scheduler.h

/*
 * \brief   Schedules CPU shares for the execution time of a CPU
 * \author  Martin Stein
 * \date    2014-10-09
 */

/*
 * Copyright (C) 2014-2017 Genode Labs GmbH
 *
 * This file is part of the Genode OS framework, which is distributed
 * under the terms of the GNU Affero General Public License version 3.
 */

#ifndef _CORE__KERNEL__CPU_SCHEDULER_H_
#define _CORE__KERNEL__CPU_SCHEDULER_H_

/* core includes */
#include <util.h>
#include <util/misc_math.h>
#include <kernel/configuration.h>
#include <kernel/double_list.h>

namespace Kernel
{
	/**
	 * Priority of an unconsumed CPU claim versus other unconsumed CPU claims
	 */
	class Cpu_priority;

	/**
	 * Scheduling context that is both claim and fill
	 */
	class Cpu_share;

	/**
	 * Schedules CPU shares for the execution time of a CPU
	 */
	class Cpu_scheduler;
}

class Kernel::Cpu_priority
{
	private:

		unsigned _value;

	public:

		enum {
			MIN = 0,
			MAX = cpu_priorities - 1,
		};

		/**
		 * Construct priority with value 'v'
		 */
		Cpu_priority(signed const v) : _value(Genode::min(v, MAX)) { }

		/*
		 * Standard operators
		 */

		Cpu_priority &operator =(signed const v)
		{
			_value = Genode::min(v, MAX);
			return *this;
		}

		operator signed() const { return _value; }
};

class Kernel::Cpu_share
{
	friend class Cpu_scheduler;

	private:

		Double_list_item<Cpu_share> _fill_item  { *this };
		Double_list_item<Cpu_share> _claim_item { *this };
		signed const                _prio;
		unsigned                    _quota;
		unsigned                    _claim;
		unsigned                    _fill       { 0 };
		bool                        _ready      { false };

	public:

		/**
		 * Constructor
		 *
		 * \param p  claimed priority
		 * \param q  claimed quota
		 */
		Cpu_share(signed const p, unsigned const q)
		: _prio(p), _quota(q), _claim(q) { }

		/*
		 * Accessors
		 */

		bool ready() const { return _ready; }
		void quota(unsigned const q) { _quota = q; }
};

class Kernel::Cpu_scheduler
{
	private:

		typedef Cpu_share    Share;
		typedef Cpu_priority Prio;

		Double_list<Cpu_share>  _rcl[Prio::MAX + 1]; /* ready claims */
		Double_list<Cpu_share>  _ucl[Prio::MAX + 1]; /* unready claims */
		Double_list<Cpu_share>  _fills { };          /* ready fills */
		Share                  &_idle;
		Share                  *_head = nullptr;
		unsigned                _head_quota  = 0;
		bool                    _head_claims = false;
		bool                    _head_yields = false;
		unsigned const          _quota;
		unsigned                _residual;
		unsigned const          _fill;
		bool                    _need_to_schedule { true };
		time_t                  _last_time { 0 };

		template <typename F> void _for_each_prio(F f) {
			for (signed p = Prio::MAX; p > Prio::MIN - 1; p--) { f(p); } }

		static void _reset(Cpu_share &share);

		void     _reset_claims(unsigned const p);
		void     _next_round();
		void     _consumed(unsigned const q);
		void     _set_head(Share &s, unsigned const q, bool const c);
		void     _next_fill();
		void     _head_claimed(unsigned const r);
		void     _head_filled(unsigned const r);
		bool     _claim_for_head();
		bool     _fill_for_head();
		unsigned _trim_consumption(unsigned &q);

		/**
		 * Fill 's' becomes a claim due to a quota donation
		 */
		void _quota_introduction(Share &s);

		/**
		 * Claim 's' looses its state as claim due to quota revokation
		 */
		void _quota_revokation(Share &s);

		/**
		 * The quota of claim 's' changes to 'q'
		 */
		void _quota_adaption(Share &s, unsigned const q);

	public:

		/**
		 * Constructor
		 *
		 * \param i  Gets scheduled with static quota when no other share
		 *           is schedulable. Unremovable. All values get ignored.
		 * \param q  total amount of time quota that can be claimed by shares
		 * \param f  time-slice length of the fill round-robin
		 */
		Cpu_scheduler(Share &i, unsigned const q, unsigned const f);

		bool need_to_schedule() { return _need_to_schedule; }
		void timeout()          { _need_to_schedule = true; }

		/**
		 * Update head according to the consumed time
		 */
		void update(time_t time);

		/**
		 * Set 's1' ready and return wether this outdates current head
		 */
		void ready_check(Share &s1);

		/**
		 * Set share 's' ready
		 */
		void ready(Share &s);

		/**
		 * Set share 's' unready
		 */
		void unready(Share &s);

		/**
		 * Current head looses its current claim/fill for this round
		 */
		void yield();

		/**
		 * Remove share 's' from scheduler
		 */
		void remove(Share &s);

		/**
		 * Insert share 's' into scheduler
		 */
		void insert(Share &s);

		/**
		 * Set quota of share 's' to 'q'
		 */
		void quota(Share &s, unsigned const q);

		/*
		 * Accessors
		 */

		Share &head() const;
		unsigned head_quota() const {
			return Genode::min(_head_quota, _residual); }
		unsigned quota() const { return _quota; }
		unsigned residual() const { return _residual; }
};

#endif /* _CORE__KERNEL__CPU_SCHEDULER_H_ */