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/*
* Dynamic queue limits (dql) - Definitions
*
* Copyright (c) 2011, Tom Herbert <therbert@google.com>
*
* 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 {
unsigned int num_queued;
unsigned int adj_limit;
unsigned int last_obj_cnt;
unsigned int limit ____cacheline_aligned_in_smp;
unsigned int num_completed;
unsigned int prev_ovlimit;
unsigned int prev_num_queued;
unsigned int prev_last_obj_cnt;
unsigned int lowest_slack;
unsigned long slack_start_time;
unsigned int max_limit;
unsigned int min_limit;
unsigned int slack_hold_time;
};
#define DQL_MAX_OBJECT (UINT_MAX / 16)
#define DQL_MAX_LIMIT ((UINT_MAX / 2) - DQL_MAX_OBJECT)
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;
}
static inline int dql_avail(const struct dql *dql)
{
return dql->adj_limit - dql->num_queued;
}
void dql_completed(struct dql *dql, unsigned int count);
void dql_reset(struct dql *dql);
int dql_init(struct dql *dql, unsigned hold_time);
#endif
#endif
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