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108 lines
3.7 KiB
108 lines
3.7 KiB
/* SPDX-License-Identifier: GPL-2.0 */ |
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/* |
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* Dynamic queue limits (dql) - Definitions |
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* |
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* Copyright (c) 2011, Tom Herbert <[email protected]> |
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* |
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* This header file contains the definitions for dynamic queue limits (dql). |
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* dql would be used in conjunction with a producer/consumer type queue |
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* (possibly a HW queue). Such a queue would have these general properties: |
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* |
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* 1) Objects are queued up to some limit specified as number of objects. |
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* 2) Periodically a completion process executes which retires consumed |
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* objects. |
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* 3) Starvation occurs when limit has been reached, all queued data has |
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* actually been consumed, but completion processing has not yet run |
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* so queuing new data is blocked. |
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* 4) Minimizing the amount of queued data is desirable. |
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* |
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* The goal of dql is to calculate the limit as the minimum number of objects |
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* needed to prevent starvation. |
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* |
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* The primary functions of dql are: |
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* dql_queued - called when objects are enqueued to record number of objects |
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* dql_avail - returns how many objects are available to be queued based |
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* on the object limit and how many objects are already enqueued |
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* dql_completed - called at completion time to indicate how many objects |
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* were retired from the queue |
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* |
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* The dql implementation does not implement any locking for the dql data |
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* structures, the higher layer should provide this. dql_queued should |
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* be serialized to prevent concurrent execution of the function; this |
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* is also true for dql_completed. However, dql_queued and dlq_completed can |
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* be executed concurrently (i.e. they can be protected by different locks). |
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*/ |
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#ifndef _LINUX_DQL_H |
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#define _LINUX_DQL_H |
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#ifdef __KERNEL__ |
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#include <asm/bug.h> |
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struct dql { |
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/* Fields accessed in enqueue path (dql_queued) */ |
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unsigned int num_queued; /* Total ever queued */ |
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unsigned int adj_limit; /* limit + num_completed */ |
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unsigned int last_obj_cnt; /* Count at last queuing */ |
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/* Fields accessed only by completion path (dql_completed) */ |
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unsigned int limit ____cacheline_aligned_in_smp; /* Current limit */ |
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unsigned int num_completed; /* Total ever completed */ |
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unsigned int prev_ovlimit; /* Previous over limit */ |
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unsigned int prev_num_queued; /* Previous queue total */ |
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unsigned int prev_last_obj_cnt; /* Previous queuing cnt */ |
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unsigned int lowest_slack; /* Lowest slack found */ |
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unsigned long slack_start_time; /* Time slacks seen */ |
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/* Configuration */ |
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unsigned int max_limit; /* Max limit */ |
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unsigned int min_limit; /* Minimum limit */ |
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unsigned int slack_hold_time; /* Time to measure slack */ |
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}; |
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/* Set some static maximums */ |
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#define DQL_MAX_OBJECT (UINT_MAX / 16) |
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#define DQL_MAX_LIMIT ((UINT_MAX / 2) - DQL_MAX_OBJECT) |
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/* |
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* Record number of objects queued. Assumes that caller has already checked |
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* availability in the queue with dql_avail. |
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*/ |
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static inline void dql_queued(struct dql *dql, unsigned int count) |
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{ |
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BUG_ON(count > DQL_MAX_OBJECT); |
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dql->last_obj_cnt = count; |
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/* We want to force a write first, so that cpu do not attempt |
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* to get cache line containing last_obj_cnt, num_queued, adj_limit |
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* in Shared state, but directly does a Request For Ownership |
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* It is only a hint, we use barrier() only. |
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*/ |
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barrier(); |
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dql->num_queued += count; |
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} |
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/* Returns how many objects can be queued, < 0 indicates over limit. */ |
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static inline int dql_avail(const struct dql *dql) |
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{ |
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return READ_ONCE(dql->adj_limit) - READ_ONCE(dql->num_queued); |
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} |
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/* Record number of completed objects and recalculate the limit. */ |
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void dql_completed(struct dql *dql, unsigned int count); |
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/* Reset dql state */ |
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void dql_reset(struct dql *dql); |
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/* Initialize dql state */ |
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void dql_init(struct dql *dql, unsigned int hold_time); |
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#endif /* _KERNEL_ */ |
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#endif /* _LINUX_DQL_H */
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