[linux.git] / include / linux / dynamic_queue_limits.h

/*
 * Dynamic queue limits (dql) - Definitions
 *
 * Copyright (c) 2011, Tom Herbert <[email protected]>
 *
 * This header file contains the definitions for dynamic queue limits (dql).
 * dql would be used in conjunction with a producer/consumer type queue
 * (possibly a HW queue).  Such a queue would have these general properties:
 *
 *   1) Objects are queued up to some limit specified as number of objects.
 *   2) Periodically a completion process executes which retires consumed
 *      objects.
 *   3) Starvation occurs when limit has been reached, all queued data has
 *      actually been consumed, but completion processing has not yet run
 *      so queuing new data is blocked.
 *   4) Minimizing the amount of queued data is desirable.
 *
 * The goal of dql is to calculate the limit as the minimum number of objects
 * needed to prevent starvation.
 *
 * The primary functions of dql are:
 *    dql_queued - called when objects are enqueued to record number of objects
 *    dql_avail - returns how many objects are available to be queued based
 *      on the object limit and how many objects are already enqueued
 *    dql_completed - called at completion time to indicate how many objects
 *      were retired from the queue
 *
 * The dql implementation does not implement any locking for the dql data
 * structures, the higher layer should provide this.  dql_queued should
 * be serialized to prevent concurrent execution of the function; this
 * is also true for  dql_completed.  However, dql_queued and dlq_completed  can
 * be executed concurrently (i.e. they can be protected by different locks).
 */

#ifndef _LINUX_DQL_H
#define _LINUX_DQL_H

#ifdef __KERNEL__

struct dql {
	/* Fields accessed in enqueue path (dql_queued) */
	unsigned int	num_queued;		/* Total ever queued */
	unsigned int	adj_limit;		/* limit + num_completed */
	unsigned int	last_obj_cnt;		/* Count at last queuing */

	/* Fields accessed only by completion path (dql_completed) */

	unsigned int	limit ____cacheline_aligned_in_smp; /* Current limit */
	unsigned int	num_completed;		/* Total ever completed */

	unsigned int	prev_ovlimit;		/* Previous over limit */
	unsigned int	prev_num_queued;	/* Previous queue total */
	unsigned int	prev_last_obj_cnt;	/* Previous queuing cnt */

	unsigned int	lowest_slack;		/* Lowest slack found */
	unsigned long	slack_start_time;	/* Time slacks seen */

	/* Configuration */
	unsigned int	max_limit;		/* Max limit */
	unsigned int	min_limit;		/* Minimum limit */
	unsigned int	slack_hold_time;	/* Time to measure slack */
};

/* Set some static maximums */
#define DQL_MAX_OBJECT (UINT_MAX / 16)
#define DQL_MAX_LIMIT ((UINT_MAX / 2) - DQL_MAX_OBJECT)

/*
 * Record number of objects queued. Assumes that caller has already checked
 * availability in the queue with dql_avail.
 */
static inline void dql_queued(struct dql *dql, unsigned int count)
{
	BUG_ON(count > DQL_MAX_OBJECT);

	dql->num_queued += count;
	dql->last_obj_cnt = count;
}

/* Returns how many objects can be queued, < 0 indicates over limit. */
static inline int dql_avail(const struct dql *dql)
{
	return dql->adj_limit - dql->num_queued;
}

/* Record number of completed objects and recalculate the limit. */
void dql_completed(struct dql *dql, unsigned int count);

/* Reset dql state */
void dql_reset(struct dql *dql);

/* Initialize dql state */
int dql_init(struct dql *dql, unsigned hold_time);

#endif /* _KERNEL_ */

#endif /* _LINUX_DQL_H */
Commit	Line	Data
75957ba3 TH	1	/*
	2	* Dynamic queue limits (dql) - Definitions
	3	*
	4	* Copyright (c) 2011, Tom Herbert <[email protected]>
	5	*
	6	* This header file contains the definitions for dynamic queue limits (dql).
	7	* dql would be used in conjunction with a producer/consumer type queue
	8	* (possibly a HW queue). Such a queue would have these general properties:
	9	*
	10	* 1) Objects are queued up to some limit specified as number of objects.
	11	* 2) Periodically a completion process executes which retires consumed
	12	* objects.
	13	* 3) Starvation occurs when limit has been reached, all queued data has
	14	* actually been consumed, but completion processing has not yet run
	15	* so queuing new data is blocked.
	16	* 4) Minimizing the amount of queued data is desirable.
	17	*
	18	* The goal of dql is to calculate the limit as the minimum number of objects
	19	* needed to prevent starvation.
	20	*
	21	* The primary functions of dql are:
	22	* dql_queued - called when objects are enqueued to record number of objects
	23	* dql_avail - returns how many objects are available to be queued based
	24	* on the object limit and how many objects are already enqueued
	25	* dql_completed - called at completion time to indicate how many objects
	26	* were retired from the queue
	27	*
	28	* The dql implementation does not implement any locking for the dql data
	29	* structures, the higher layer should provide this. dql_queued should
	30	* be serialized to prevent concurrent execution of the function; this
	31	* is also true for dql_completed. However, dql_queued and dlq_completed can
	32	* be executed concurrently (i.e. they can be protected by different locks).
	33	*/
	34
	35	#ifndef _LINUX_DQL_H
	36	#define _LINUX_DQL_H
	37
	38	#ifdef __KERNEL__
	39
	40	struct dql {
	41	/* Fields accessed in enqueue path (dql_queued) */
	42	unsigned int num_queued; /* Total ever queued */
	43	unsigned int adj_limit; /* limit + num_completed */
	44	unsigned int last_obj_cnt; /* Count at last queuing */
	45
	46	/* Fields accessed only by completion path (dql_completed) */
	47
	48	unsigned int limit ____cacheline_aligned_in_smp; /* Current limit */
	49	unsigned int num_completed; /* Total ever completed */
	50
	51	unsigned int prev_ovlimit; /* Previous over limit */
	52	unsigned int prev_num_queued; /* Previous queue total */
	53	unsigned int prev_last_obj_cnt; /* Previous queuing cnt */
	54
	55	unsigned int lowest_slack; /* Lowest slack found */
	56	unsigned long slack_start_time; /* Time slacks seen */
	57
	58	/* Configuration */
	59	unsigned int max_limit; /* Max limit */
	60	unsigned int min_limit; /* Minimum limit */
	61	unsigned int slack_hold_time; /* Time to measure slack */
	62	};
	63
	64	/* Set some static maximums */
65	#define DQL_MAX_OBJECT (UINT_MAX / 16)
66	#define DQL_MAX_LIMIT ((UINT_MAX / 2) - DQL_MAX_OBJECT)
67
68	/*
69	* Record number of objects queued. Assumes that caller has already checked
70	* availability in the queue with dql_avail.
71	*/
72	static inline void dql_queued(struct dql *dql, unsigned int count)
73	{
74	BUG_ON(count > DQL_MAX_OBJECT);
75
76	dql->num_queued += count;
77	dql->last_obj_cnt = count;
78	}
79
80	/* Returns how many objects can be queued, < 0 indicates over limit. */
81	static inline int dql_avail(const struct dql *dql)
82	{
83	return dql->adj_limit - dql->num_queued;
84	}
85
86	/* Record number of completed objects and recalculate the limit. */
87	void dql_completed(struct dql *dql, unsigned int count);
88
89	/* Reset dql state */
90	void dql_reset(struct dql *dql);
91
92	/* Initialize dql state */
93	int dql_init(struct dql *dql, unsigned hold_time);
94
95	#endif /* _KERNEL_ */
96
97	#endif /* _LINUX_DQL_H */