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1 : : /* SPDX-License-Identifier: GPL-2.0 */ 2 : : /* 3 : : * Dynamic queue limits (dql) - Definitions 4 : : * 5 : : * Copyright (c) 2011, Tom Herbert <therbert@google.com> 6 : : * 7 : : * This header file contains the definitions for dynamic queue limits (dql). 8 : : * dql would be used in conjunction with a producer/consumer type queue 9 : : * (possibly a HW queue). Such a queue would have these general properties: 10 : : * 11 : : * 1) Objects are queued up to some limit specified as number of objects. 12 : : * 2) Periodically a completion process executes which retires consumed 13 : : * objects. 14 : : * 3) Starvation occurs when limit has been reached, all queued data has 15 : : * actually been consumed, but completion processing has not yet run 16 : : * so queuing new data is blocked. 17 : : * 4) Minimizing the amount of queued data is desirable. 18 : : * 19 : : * The goal of dql is to calculate the limit as the minimum number of objects 20 : : * needed to prevent starvation. 21 : : * 22 : : * The primary functions of dql are: 23 : : * dql_queued - called when objects are enqueued to record number of objects 24 : : * dql_avail - returns how many objects are available to be queued based 25 : : * on the object limit and how many objects are already enqueued 26 : : * dql_completed - called at completion time to indicate how many objects 27 : : * were retired from the queue 28 : : * 29 : : * The dql implementation does not implement any locking for the dql data 30 : : * structures, the higher layer should provide this. dql_queued should 31 : : * be serialized to prevent concurrent execution of the function; this 32 : : * is also true for dql_completed. However, dql_queued and dlq_completed can 33 : : * be executed concurrently (i.e. they can be protected by different locks). 34 : : */ 35 : : 36 : : #ifndef _LINUX_DQL_H 37 : : #define _LINUX_DQL_H 38 : : 39 : : #ifdef __KERNEL__ 40 : : 41 : : struct dql { 42 : : /* Fields accessed in enqueue path (dql_queued) */ 43 : : unsigned int num_queued; /* Total ever queued */ 44 : : unsigned int adj_limit; /* limit + num_completed */ 45 : : unsigned int last_obj_cnt; /* Count at last queuing */ 46 : : 47 : : /* Fields accessed only by completion path (dql_completed) */ 48 : : 49 : : unsigned int limit ____cacheline_aligned_in_smp; /* Current limit */ 50 : : unsigned int num_completed; /* Total ever completed */ 51 : : 52 : : unsigned int prev_ovlimit; /* Previous over limit */ 53 : : unsigned int prev_num_queued; /* Previous queue total */ 54 : : unsigned int prev_last_obj_cnt; /* Previous queuing cnt */ 55 : : 56 : : unsigned int lowest_slack; /* Lowest slack found */ 57 : : unsigned long slack_start_time; /* Time slacks seen */ 58 : : 59 : : /* Configuration */ 60 : : unsigned int max_limit; /* Max limit */ 61 : : unsigned int min_limit; /* Minimum limit */ 62 : : unsigned int slack_hold_time; /* Time to measure slack */ 63 : : }; 64 : : 65 : : /* Set some static maximums */ 66 : : #define DQL_MAX_OBJECT (UINT_MAX / 16) 67 : : #define DQL_MAX_LIMIT ((UINT_MAX / 2) - DQL_MAX_OBJECT) 68 : : 69 : : /* 70 : : * Record number of objects queued. Assumes that caller has already checked 71 : : * availability in the queue with dql_avail. 72 : : */ 73 : 0 : static inline void dql_queued(struct dql *dql, unsigned int count) 74 : : { 75 [ # # # # ]: 0 : BUG_ON(count > DQL_MAX_OBJECT); 76 : : 77 : 0 : dql->last_obj_cnt = count; 78 : : 79 : : /* We want to force a write first, so that cpu do not attempt 80 : : * to get cache line containing last_obj_cnt, num_queued, adj_limit 81 : : * in Shared state, but directly does a Request For Ownership 82 : : * It is only a hint, we use barrier() only. 83 : : */ 84 : 0 : barrier(); 85 : : 86 [ # # ]: 0 : dql->num_queued += count; 87 : : } 88 : : 89 : : /* Returns how many objects can be queued, < 0 indicates over limit. */ 90 : 166 : static inline int dql_avail(const struct dql *dql) 91 : : { 92 [ # # # # ]: 166 : return READ_ONCE(dql->adj_limit) - READ_ONCE(dql->num_queued); 93 : : } 94 : : 95 : : /* Record number of completed objects and recalculate the limit. */ 96 : : void dql_completed(struct dql *dql, unsigned int count); 97 : : 98 : : /* Reset dql state */ 99 : : void dql_reset(struct dql *dql); 100 : : 101 : : /* Initialize dql state */ 102 : : void dql_init(struct dql *dql, unsigned int hold_time); 103 : : 104 : : #endif /* _KERNEL_ */ 105 : : 106 : : #endif /* _LINUX_DQL_H */